AHFS Class:

• HIV Protease Inhibitors 8:18.08.08

Generic Name(s):

• Ritonavir

Ritonavir, an antiretroviral agent, is a human immunodeficiency virus (HIV) protease inhibitor (PI).1

Treatment of HIV Infection

Ritonavir is used in conjunction with other antiretroviral agents for the treatment of human immunodeficiency virus type 1 (HIV-1) infection in adults, adolescents, and pediatric patients older than 1 month of age.1

Regimens that contain full-dose ritonavir or ritonavir as the sole HIV protease inhibitor (PI) are not recommended for initial treatment because of a high pill burden, GI intolerance, and metabolic toxicity.200,201 Low-dose ritonavir is commonly used in conjunction with other PIs as a pharmacokinetic enhancer (booster) to decrease metabolism of and increase plasma concentrations of the other PI; consult guidelines for the most current information on recommended regimens.200,201,202

Antiretroviral-naïve Adults and Adolescents

Safety and efficacy of ritonavir for antiretroviral therapy in antiretroviral-naïve adults were initially evaluated in a randomized, double-blind study (study 245) that used regimens that are no longer considered standard of care (monotherapy, 2-drug regimens).1 Patients in this study had mild to moderate HIV infection (mean baseline CD4+ T-cell counts 364/mm³) and were randomized to receive monotherapy with oral ritonavir (600 mg twice daily), monotherapy with oral zidovudine (200 mg 3 times daily), or a 2-drug regimen of oral ritonavir (600 mg twice daily) and oral zidovudine (200 mg 3 times daily).1 During the double-blind phase of the study, ritonavir monotherapy was associated with greater mean increases in CD4+ T-cell count from baseline to week 12 compared with the zidovudine arms; mean CD4+ T-cell count then appeared to plateau through week 24 in those receiving ritonavir monotherapy, but gradually diminished through week 24 in those receiving zidovudine monotherapy or the regimen that included both drugs.1 From baseline to week 2, greater mean decreases in plasma HIV-1 RNA levels were observed in those receiving ritonavir or the 2-drug regimen containing ritonavir compared with those receiving zidovudine monotherapy.1 After week 2 and through week 24, mean plasma HIV-1 RNA levels remained stable in those receiving ritonavir or zidovudine monotherapy or gradually rebounded toward baseline in those receiving both drugs.1

Antiretroviral-experienced Adults and Adolescents

Safety and efficacy of ritonavir for use in previously treated HIV-infected patients were initially evaluated in a randomized, double-blind study with open-label follow-up (study 247) that used regimens that are no longer considered standard of care (monotherapy, 2-drug regimens).1,129 The study involved 1090 patients with advanced HIV infection (baseline CD4+ T-cell count 100/mm³ or less; mean baseline count 32/mm³) who had received at least 9 months of nucleoside reverse transcriptase inhibitor (NRTI) therapy.1,129 Oral ritonavir (600 mg twice daily) or placebo was added to the patient's existing regimen, which may have consisted of up to 2 approved antiretroviral agents (e.g., zidovudine, zalcitabine [no longer commercially available in the US], didanosine, stavudine [no longer commercially available in the US]); efficacy was assessed by disease progression or death over the following 6 months.1,129

At week 24, patients who received ritonavir in conjunction with their existing regimen had clinically important increases in CD4+ T-cell counts; there were no improvements in these surrogate markers in patients randomized to receive placebo in addition to their existing regimen.1 The cumulative incidence of clinical disease progression or death during the double-blind phase (median duration 6 months) was 26% in patients randomized to receive ritonavir in conjunction with their existing regimen and 42% in those randomized to receive placebo with the existing regimen.1 The cumulative mortality through the end of the open-label follow-up phase (median duration 13.5 or 14 months) was 18 or 26% in patients randomized to receive ritonavir or placebo, respectively, in conjunction with their existing regimen.1 During the double-blind phase of the study, increases in CD4+ T-cell counts were observed at week 2 and 4 in those receiving ritonavir, and mean CD4+ T-cell count then appeared to plateau from week 4 through week 24.1 In contrast, there was no apparent change in mean CD4+ T-cell count at any visit between baseline and week 24 in patients randomized to placebo.1

Pediatric Patients

Safety and efficacy of ritonavir in children 2-17 years of age were evaluated in a randomized, phase 2 study (PACTG 338) that used regimens that are no longer considered standard of care (monotherapy, 2-drug regimens).94 In this study, HIV-infected children who had received prior antiretroviral therapy (86% had previously received zidovudine alone or in conjunction with didanosine) were randomized to receive a 2-drug regimen of zidovudine and lamivudine, a 2-drug regimen of ritonavir and stavudine, or a 3-drug regimen of zidovudine, lamivudine, and ritonavir (350 mg/m² twice daily).94 At week 12, interim analysis indicated that only 14% of those receiving zidovudine and lamivudine had undetectable levels of plasma HIV-1 RNA (i.e., less than 400 copies/mL) whereas 57 or 61% of those receiving the 2- or 3-drug regimen containing ritonavir, respectively, had undetectable levels.94 In the subgroup of children who had undetectable plasma HIV-1 RNA levels at study entry, 27% of those receiving the 2-drug ritonavir regimen and 42% of those receiving the 3-drug ritonavir regimen had undetectable levels at 48 weeks.94 The virologic response to the ritonavir-containing regimens was lower in those with a higher viral load at study entry.94 In the subgroups of children who had baseline plasma HIV-1 RNA levels of 2.6-3, 3-4, 4-5, or 5-6 log₁₀ copies/mL, plasma HIV-1 RNA levels were undetectable at 48 weeks in 69, 44, 32, or 19%, respectively, in those receiving the 2- or 3-drug ritonavir regimens.94

Efficacy of ritonavir in conjunction with zidovudine and lamivudine was evaluated in an open-label, phase 1 and 2 study in HIV-infected infants 1-24 months of age who had not previously received therapy with a PI.183 At week 16, 36 of 43 children who continued study treatment (as-treated analysis) had plasma HIV-1 RNA levels less than 400 copies/mL.183 At week 104, durable viral suppression was maintained in 46% of children (as-treated analysis).183

The efficacy, safety, and pharmacokinetics of ritonavir have been evaluated in a multicenter phase 1 and 2 study in HIV-infected children 6 months to 18 years of age who were treatment-naïve or who had become refractory or intolerant to previous antiretroviral therapy.77 These children received ritonavir monotherapy (250-400 mg/m² twice daily) for the first 12 weeks, then zidovudine (90 mg/m² every 6 hours) and/or didanosine (90 mg/m² twice daily) was added to the regimen.77,90 Interim analysis at 24 weeks of data from children 2 years of age or older (younger children were excluded from this analysis) indicate that regimens that included ritonavir in a dosage of 300 mg/m² twice daily in conjunction with zidovudine and/or didanosine were associated with a mean increase in CD4+ T-cell counts of 263/mm³ from baseline counts and a mean decrease in plasma HIV-1 RNA levels of 0.4 logs/mL from baseline levels.90

Clinical Perspective

Therapeutic options for the treatment and prevention of HIV infection and recommendations concerning the use of antiretrovirals are continuously evolving.200,201,202 Antiretroviral therapy is recommended for all individuals with HIV regardless of CD4 counts, and should be initiated as soon as possible after diagnosis of HIV and continued indefinitely.200,201,202 The primary goals of antiretroviral therapy are to achieve and maintain durable suppression of HIV viral load (as measured by plasma HIV-1 RNA levels) to a level below which drug-resistance mutations cannot emerge (i.e., below detectable limits), restore and preserve immunologic function, reduce HIV-related morbidity and mortality, improve quality of life, and prevent transmission of HIV.200,202 While the most appropriate antiretroviral regimen cannot be defined for each clinical scenario, the US Department of Health and Human Services (HHS) Panel on Antiretroviral Guidelines for Adults and Adolescents, HHS Panel on Antiretroviral Therapy and Medical Management of Children Living with HIV, and HHS Panel on Treatment of Pregnant Women with HIV Infection and Prevention of Perinatal Transmission, have developed comprehensive guidelines that provide information on selection and use of antiretrovirals for the treatment or prevention of HIV infection.200,201,202 Because of the complexity of managing patients with HIV, it is recommended that clinicians with HIV expertise be consulted when needed.200,201,202

The use of combination antiretroviral regimens that generally include 3 drugs from 2 or more drug classes is currently recommended to achieve viral suppression.200,201 In both treatment-naïve adults and children, an initial antiretroviral regimen generally consists of 2 NRTIs administered in combination with a third active antiretroviral drug from 1 of 3 drug classes: an integrase strand transfer inhibitor (INSTI), a non-nucleoside reverse transcriptase inhibitor (NNRTI), or a PI with a pharmacokinetic enhancer (also known as a booster; the 2 drugs used for this purpose are cobicistat and ritonavir).200,201,202 Selection of an initial antiretroviral regimen should be individualized based on factors such as virologic efficacy, toxicity, pill burden, dosing frequency, drug-drug interaction potential, resistance test results, comorbid conditions, access, and cost.200,201,202 In patients with comorbid infections (e.g., hepatitis B, tuberculosis), antiretroviral regimen selection should also consider the potential for activity against other present infections and timing of initiation relative to other anti-infective regimens.200

Regimens that contain full-dose ritonavir or ritonavir as the sole HIV PI are not recommended for initial treatment because of a high pill burden, GI intolerance, and metabolic toxicity.200,201 Low-dose ritonavir is used in conjunction with other PIs to decrease metabolism of and increase plasma concentrations of the other PI.200,201 Use of low-dose ritonavir in conjunction with another PI has been referred to as ritonavir pharmacokinetic enhancement or ritonavir-boosted therapy.200,201 The antiretroviral activity of these regimens is due to the other PI since a therapeutic dosage of ritonavir is not administered.200,201 A fixed-combination preparation of lopinavir and low-dose ritonavir is commercially available (lopinavir/ritonavir); other ritonavir-boosted regimens involve administration of a specific dosage of ritonavir and the other PI recommended for the combined regimen.200,201

In the 2024 HHS adult and adolescent HIV treatment guideline, ritonavir is included in various antiretroviral regimens as a pharmacokinetic enhancer for certain PIs.200 Some of these ritonavir-containing regimens are listed among recommended initial regimens for most people with HIV or recommended initial regimens in certain clinical situations.200 For patients with HIV and a history of long-acting cabotegravir use for pre-exposure prophylaxis (PrEP), INSTI genotypic resistance testing is recommended prior to initiation of antiretroviral therapy; however, if treatment is begun before the results of genotypic testing are known, a 3-drug regimen of ritonavir- or cobicistat-boosted darunavir, tenofovir, and emtricitabine or lamivudine is recommended.200 In certain clinical situations, recommended regimens for initial HIV treatment include the following: ritonavir- or cobicistat-boosted darunavir plus tenofovir plus emtricitabine or lamivudine; ritonavir- or cobicistat-boosted atazanavir plus tenofovir plus emtricitabine or lamivudine; or, if HLA-B*5701 negative, ritonavir- or cobicistat-boosted darunavir plus abacavir plus lamivudine.200

In the 2024 HHS pediatric HIV treatment guideline, ritonavir is included in various antiretroviral regimens as a pharmacokinetic enhancer for certain PIs.201 Lopinavir/ritonavir plus 2 NRTIs is an alternative regimen in patients ≥14 days to <30 days of age weighing ≥2 kg.201 Lopinavir/ritonavir plus 2 NRTIs is also a recommended alternative regimen for pediatric patients ≥30 days to <2 years of age.201 Ritonavir-boosted atazanavir plus 2 NRTIs is a recommended alternative regimen for pediatric patients ≥2 years of age, and ritonavir-boosted darunavir plus 2 NRTIs is a recommended alternative regimen for pediatric patients ≥2 years of age.201

In the 2024 HHS perinatal HIV treatment guideline, ritonavir is included in various antiretroviral regimens as a pharmacokinetic enhancer for certain PIs.202 Ritonavir-boosted darunavir plus tenofovir plus emtricitabine or lamivudine is a preferred regimen for initial treatment of pregnant patients with early HIV infection and a history of long-acting cabotegravir exposure for PrEP.202 Otherwise, ritonavir-containing regimens are only recommended as alternative therapy in pregnant patients; recommended alternative regimens include ritonavir-boosted atazanavir plus a preferred dual NRTI backbone or ritonavir-boosted darunavir plus a preferred dual NRTI backbone.202

Postexposure Prophylaxis following Occupational Exposure to HIV

Ritonavir is used as a pharmacokinetic enhancer in conjunction with other antiretrovirals for postexposure prophylaxis of HIV infection following occupational exposure† (PEP) in health-care personnel and other individuals exposed via percutaneous injury (e.g., needlestick, cut with sharp object) or mucous membrane or nonintact skin (e.g., chapped, abraded, dermatitis) contact with blood, tissue, or other body fluids that might contain HIV.199

The US Public Health Service (USPHS) states that the preferred regimen for PEP following an occupational exposure to HIV is a 3-drug regimen of raltegravir used in conjunction with emtricitabine and tenofovir disoproxil fumarate (tenofovir DF; may be administered as the fixed combination emtricitabine/tenofovir DF; Truvada^®).199 These experts recommend several alternative regimens that include an INSTI, NNRTI, or PI and 2 NRTIs (dual NRTIs).199 Recommended alternatives to raltegravir (to be given in conjunction with 2 NRTIs) include ritonavir-boosted darunavir, etravirine, rilpivirine, ritonavir-boosted atazanavir, and lopinavir/ritonavir.199

Because management of occupational exposures to HIV is complex and evolving, consultation with an infectious diseases specialist, clinician with expertise in administration of antiretroviral agents, and/or the National Clinicians' Postexposure Prophylaxis Hotline (PEPline at 888-448-4911) is recommended whenever possible.199 However, initiation of PEP should not be delayed while waiting for expert consultation.199

Postexposure Prophylaxis following Nonoccupational Exposure to HIV

Ritonavir is used as a pharmacokinetic enhancer in conjunction with other antiretrovirals for postexposure prophylaxis of HIV infection following nonoccupational exposure† (nPEP) in individuals exposed to blood, genital secretions, or other potentially infectious body fluids that might contain HIV when that exposure represents a substantial risk for HIV transmission.198

When nPEP is indicated following a nonoccupational exposure to HIV, the US Centers for Disease Control and Prevention (CDC) states that the preferred regimen in adults and adolescents 13 years of age or older with normal renal function is either raltegravir or dolutegravir used in conjunction with emtricitabine and tenofovir DF (administered as the fixed combination emtricitabine/tenofovir DF; Truvada^®).198 The alternative nPEP regimen recommended in these patients is ritonavir-boosted darunavir used in conjunction with emtricitabine/tenofovir DF (Truvada^®).198

Consultation with an infectious diseases specialist, clinician with expertise in administration of antiretroviral agents, and/or the National Clinicians' Postexposure Prophylaxis Hotline (PEPline at 888-448-4911) is recommended if nPEP is indicated in certain exposed individuals (e.g., pregnant women, children, those with medical conditions such as renal impairment) or if an antiretroviral regimen not included in the CDC guidelines is being considered, the source virus is known or likely to be resistant to antiretrovirals, or the healthcare provider is inexperienced in prescribing antiretrovirals.198 However, initiation of nPEP should not be delayed while waiting for expert consultation.198

General

Pretreatment Screening

• Evaluate serum triglyceride and serum cholesterol concentrations prior to initiation of ritonavir therapy.1
• Ritonavir use has been associated with changes in serum AST, ALT, γ-glutamyltransferase (GGT), creatine phosphokinase (CPK), and uric acid.1 Perform appropriate laboratory tests prior to initiation of therapy.1

Patient Monitoring

• Consider monitoring for hyperglycemia, new-onset diabetes mellitus, or exacerbation of preexisting diabetes mellitus in patients receiving ritonavir.1
• Monitor serum triglyceride and serum cholesterol concentrations at periodic intervals during ritonavir therapy.1
• Monitor appropriate laboratory tests (e.g., AST, ALT, GGT, CPK, uric acid) periodically after initiation of therapy, and when clinical signs and symptoms occur.1
• Clinical monitoring recommended when ritonavir is used concomitantly with drugs that prolong the PR interval (including calcium channel blockers, ß-adrenergic blockers, digoxin, atazanavir), particularly when used concomitantly with drugs metabolized by cytochrome P-450 (CYP) isoenzyme 3A.1

Dispensing and Administration Precautions

• The Institute for Safe Medication Practices (ISMP) list of error-prone abbreviations, symbols, and dose designations states that the use of abbreviations for antiretroviral medications (e.g., DOR, TAF, TDF) during the medication use process should be avoided as their use has been associated with serious medication errors.203

Other General Considerations

• Use with caution in patients with preexisting liver disease, liver enzyme abnormalities, or coinfection with hepatitis B virus (HBV) or hepatitis C virus (HCV).1 Consider more frequent testing of serum AST and ALT concentrations in these patients, especially during the first 3 months of therapy.1
• Use ritonavir with caution in patients with structural heart disease, cardiac conduction abnormalities, ischemic heart disease, and cardiomyopathies.1

Administration

Ritonavir may be administered orally as film-coated tablets or oral powder.1 The oral powder is only labeled for use in pediatric patients, and should not be used in adults.1

Ritonavir must be given in combination with other antiretrovirals for the treatment of HIV-1 infection.1

Tablets

Ritonavir tablets should be taken with meals.1

The tablets should be swallowed whole, and should not be chewed, broken, or crushed.1

Store ritonavir tablets at room temperature at ≤30°C; exposure to temperatures up to 50°C for 7 days is permitted.1 Ritonavir tablets should be dispensed in the original container or in USP equivalent tight containers (not exceeding 60 mL).1 Exposure to high humidity for longer than 2 weeks outside such containers is not recommended.1

Oral Powder

Ritonavir oral powder should be taken with meals.1 Administration with meals may also lessen the bitter aftertaste of the oral powder.1

Ritonavir oral powder should only be used for dosing increments of 100 mg; do not use for doses <100 mg or for dose increments between 100 mg intervals.1

The manufacturer states that the oral powder must be mixed with a soft food (e.g., applesauce, vanilla pudding) or a liquid (e.g., water, chocolate milk, infant formula).1 Once mixed with food or liquid, the ritonavir mixture must be administered within 2 hours.1 Discard the mixture if not administered within 2 hours of mixing.1

Ritonavir oral powder may be administered via feeding tube after mixing with water.1

Store ritonavir oral powder at ≤30°C.1

Dosage

Ritonavir must be given in conjunction with other antiretrovirals.1 Low-dose ritonavir is used with certain PIs (atazanavir, darunavir, fosamprenavir) in ritonavir-boosted regimens.200,201

If using full-dose ritonavir, initiate therapy using a dose escalation schedule to minimize nausea.1

Pediatric Dosage

Treatment of HIV Infection

When low-dose ritonavir is used with another human immunodeficiency virus (HIV) protease inhibitor (PI) as a pharmacokinetic enhancer ( ritonavir-boosted PI) in pediatric patients, the dosage of ritonavir varies and is specific to the drug combination that is used.201 (For further information regarding dosage of ritonavir-boosted PIs, see the specific HIV protease inhibitor monograph in 8:18.08.)

If ritonavir is used as the sole PI in multiple-drug regimens for the treatment of HIV-1 infection (full-dose ritonavir) in pediatric patients older than 1 month of age, the manufacturer recommends a dosage of 350-400 mg/m² twice daily (not to exceed 600 mg twice daily).1 To minimize nausea that may occur when full-dose ritonavir is initiated, use of a dose escalation schedule is recommended.1 The manufacturer recommends that full-dose ritonavir therapy in pediatric patients older than 1 month of age be initiated with a dosage of 250 mg/m² twice daily and then increased at 2- to 3-day intervals by 50 mg/m² twice daily.1

If a child is unable to tolerate a dosage of 400 mg/m² twice daily because of adverse effects, the highest dose that is tolerated may be used for maintenance therapy in conjunction with other antiretroviral agents; however, alternative therapy should be considered.1

Adult Dosage

Treatment of HIV Infection

When low-dose ritonavir is used with another HIV PI as a pharmacokinetic enhancer ( ritonavir-boosted PI) in adult patients, it is usually given in a dosage ranging from 100—400 mg daily.200 (For further information regarding dosage of ritonavir-boosted PIs, see the specific HIV protease inhibitor monograph in 8:18.08.)

If ritonavir is used as the sole HIV PI in multiple-drug regimens for the treatment of HIV type 1 (HIV-1) infection (full-dose ritonavir) in adults and adolescents, the manufacturer recommends a dosage of 600 mg twice daily.1 Because nausea may occur when full-dose ritonavir therapy is initiated, use of a dose escalation schedule is recommended to minimize adverse GI effects.1 If such a schedule is followed, the manufacturer recommends that ritonavir therapy be initiated with a minimum dosage of 300 mg twice daily and dosage increased at 2- to 3-day intervals by 100 mg twice daily up to a maximum dosage of 600 mg twice daily.1

Special Populations

Hepatic Impairment

Ritonavir dosage adjustments are not necessary in patients with mild or moderate hepatic impairment (Child-Pugh class A or B).1 However, patients with moderate hepatic impairment should be carefully monitored since lower plasma concentrations of ritonavir have been reported in these patients compared with those with normal hepatic function.1 Ritonavir is not recommended in patients with severe hepatic impairment (Child-Pugh class C).1

Renal Impairment

Although the pharmacokinetics of ritonavir have not been studied in patients with renal impairment, renal clearance of the drug is negligible and the manufacturer states that clinically important decreases in ritonavir clearance are not anticipated if the drug is administered to patients with renal impairment.1

Geriatric Patients

The manufacturer states that generally, caution should be exerted with dosage selection in geriatric patients.1 Initiate therapy at the lower end of the dosing range because of age-related decreases in hepatic, renal, and/or cardiac function and concomitant disease and drug therapy.1

Contraindications

• Known hypersensitivity (e.g., toxic epidermal necrolysis, Stevens-Johnson syndrome) to ritonavir or any ingredient in the formulation.1
• Concomitant use with drugs highly dependent on cytochrome P-450 (CYP) isoenzyme 3A for clearance and for which elevated plasma concentrations are associated with serious and/or life-threatening events (e.g., alfuzosin, amiodarone, cisapride, colchicine, dronedarone, ergot alkaloids, flecainide, lomitapide, lovastatin, lurasidone, oral midazolam, pimozide, propafenone, quinidine, ranolazine, sildenafil used for treatment of pulmonary arterial hypertension [PAH], simvastatin, triazolam, and voriconazole).1
• Concomitant use with drugs that are potent CYP3A inducers where significantly reduced ritonavir plasma concentrations may be associated with a potential loss of virologic response and possible development of resistance and cross-resistance (e.g., apalutamide, St. John's wort [ Hypericum perforatum ]).1

Warnings/Precautions

Warnings

Risk of Serious Adverse Reactions Due to Drug Interactions

A boxed warning regarding the risk of serious and/or life-threatening adverse effects due to clinically significant drug interactions resulting from concomitant use of ritonavir with a wide variety of drugs is included in the prescribing information for ritonavir.1 Review medications taken by patient before prescribing ritonavir or when prescribing other drugs for patients already receiving ritonavir.1 Initiation of ritonavir, a CYP3A inhibitor, in patients receiving medications metabolized by CYP3A or initiation of medications metabolized by CYP3A in patients already receiving ritonavir, may increase plasma concentrations of medications metabolized by CYP3A.1 Initiation of medications that inhibit or induce CYP3A may increase or decrease concentrations of ritonavir, respectively.1 These interactions may lead to clinically significant adverse reactions, potentially leading to severe, life-threatening, or fatal events from greater exposures of concomitant medications; clinically significant adverse reactions from greater exposures of ritonavir; or loss of therapeutic effect of ritonavir and possible development of resistance.1 In some cases, concomitant use is contraindicated.1 In other cases, dosage adjustment of ritonavir and/or the other drug may be necessary to manage the drug interaction.1 Because there is a high probability of drug interactions when ritonavir is used concomitantly with other drugs, patients should be instructed to inform their clinicians of their use of other drugs, including prescription and nonprescription drugs, or dietary or herbal supplements such as St. John's wort ( Hypericum perforatum ).1

The manufacturer cautions that therapeutic drug concentration monitoring and/or increased monitoring of therapeutic and adverse effects is necessary when ritonavir is used with certain other drugs, especially those with a narrow therapeutic margin (e.g., oral anticoagulants, anticonvulsants, antiarrhythmics).1 Concomitant use of ritonavir with alfuzosin, amiodarone, cisapride, dronedarone, ergot alkaloids (dihydroergotamine, ergotamine, methylergonovine), flecainide, lomitapide, lovastatin, lurasidone, oral midazolam, pimozide, propafenone, quinidine, ranolazine, sildenafil used for the treatment of pulmonary arterial hypertension (PAH), simvastatin, or triazolam is contraindicated because such use is likely to produce substantially increased plasma concentrations of these drugs and possibly precipitate serious and/or life-threatening arrhythmogenic, hematologic, neurologic, or other toxicities.1 Concomitant use of ritonavir and colchicine is contraindicated in patients with renal and/or hepatic dysfunction due to the potential for serious and/or life-threatening reactions from increased colchicine concentrations.1 Concomitant use of ritonavir (400 mg twice daily or greater) with voriconazole is contraindicated; concomitant use of ritonavir (100 mg) with voriconazole is not recommended unless potential benefits outweigh risks.1 Because St. John's wort and apalutamide may cause decreased ritonavir concentrations from potent induction of CYP3A with possible loss of virologic response and development of drug resistance, concomitant use of St. John's wort or apalutamide and ritonavir is contraindicated.

Other Warnings and Precautions

Hepatic Effects

Hepatic aminotransferase elevations exceeding 5 times the upper limit of normal (ULN), clinical hepatitis, and jaundice have occurred in patients receiving full-dose ritonavir alone or in conjunction with other antiretroviral agents.1 In clinical studies in HIV-infected individuals, increased serum concentrations of AST (SGOT) (exceeding 180 IU/L) or ALT (SGPT) (exceeding 215 IU/L) occurred in 5.3-9.5 or 5.3-9.2%, respectively, and increased serum concentrations of γ-glutamyltransferase (GGT, GGTP) (exceeding 300 IU/L) occurred in 1.8-19.6% of patients receiving ritonavir.1 The manufacturer suggests that there may be an increased risk for transaminase elevations during ritonavir therapy in patients with underlying hepatitis B virus (HBV) or hepatitis C virus (HCV) coinfection.1

There have been postmarketing reports of hepatic dysfunction, including some fatalities, in patients receiving ritonavir.1 These generally occurred in patients receiving multiple drugs and/or with advanced acquired immunodeficiency syndrome (AIDS).1

Because there have been reports of hepatic dysfunction, including some fatalities, in patients receiving ritonavir, the drug should be used with caution in patients with preexisting liver disease, liver enzyme abnormalities, or hepatitis and consideration should be given to more frequent testing of serum AST and ALT concentrations in these patients, especially during the first 3 months of therapy.1

Pancreatitis

Pancreatitis, including some fatalities, has been reported in patients receiving ritonavir, including some patients who developed hypertriglyceridemia.1 Patients with advanced HIV may be at an increased risk of triglyceride elevations and pancreatitis.1

Patients who develop clinical signs or symptoms suggestive of pancreatitis (nausea, vomiting, abdominal pain, increased serum lipase or amylase concentrations) should be evaluated and ritonavir therapy should be discontinued if a diagnosis of pancreatitis is made.1

Allergic Reactions/Hypersensitivity

Allergic reactions, including urticaria, mild skin eruptions, bronchospasm, and angioedema, have been reported in patients receiving ritonavir.1 Anaphylaxis, toxic epidermal necrolysis, and Stevens-Johnson syndrome have been reported.1 Discontinue treatment with ritonavir if severe sensitivity reactions occur.1

PR Interval Prolongation

Prolongation of the PR interval has occurred in individuals receiving ritonavir.1 Second- or third-degree AV block has been reported in patients receiving ritonavir during postmarketing experience.1

Ritonavir should be used with caution in patients with structural heart disease, cardiac conduction abnormalities, ischemic heart disease, or cardiomyopathies; these individuals may be at increased risk for cardiac conduction abnormalities.1 Caution is advised if ritonavir is used with other drugs that prolong the PR interval (e.g., some β-adrenergic blocking agents, digoxin, calcium-channel blockers, atazanavir), especially drugs metabolized by CYP3A.1 Patients should be advised to consult their clinician if they experience dizziness, lightheadedness, heart rhythm changes, or loss of consciousness.1

Lipid Disorders

Because substantial increases in serum triglyceride and serum cholesterol concentrations have been reported in patients receiving ritonavir alone or in conjunction with other antiretroviral agents (i.e., saquinavir), serum triglyceride and cholesterol concentrations should be evaluated prior to and at periodic intervals during ritonavir therapy.1 Lipid disorders should be managed by appropriate interventions; the fact that concomitant use of ritonavir and some antilipemic agents (e.g., lovastatin, simvastatin) is contraindicated or not recommended should be considered.1

Diabetes Mellitus/Hyperglycemia

Hyperglycemia, new-onset diabetes mellitus, or exacerbation of preexisting diabetes mellitus in HIV-infected individuals receiving a PI has been reported during postmarketing experience.1 In some patients, insulin or oral hypoglycemic agent therapy had to be initiated or dosage adjusted.1 In most patients who discontinued PI therapy, the hyperglycemic or diabetic episode resolved; however, hyperglycemia persisted in some patients, including a few without a known history of diabetes at baseline.1 A causal relationship between these episodes and PI therapy has not been established.1 Consider monitoring patients treated with ritonavir for hyperglycemia, new onset diabetes mellitus, or exacerbation of existing diabetes mellitus.1

Immune Reconstitution Syndrome

Patients receiving combination antiretroviral therapy may experience an immune reconstitution syndrome during the initial phase of therapy.1 Patients whose immune system responds to antiretroviral therapy may develop an inflammatory response to indolent or residual opportunistic infections (e.g., Mycobacterium avium complex [MAC], M. tuberculosis , cytomegalovirus [CMV], Pneumocystis jirovecii [formerly P. carinii ]); this may necessitate further evaluation and treatment.1

Autoimmune disorders (e.g., Graves' disease, polymyositis, Guillain-Barré syndrome) have been reported in the setting of immune reconstitution; however, the time to onset is more variable and can occur many months after initiation of antiretroviral therapy.1

Fat Redistribution

Redistribution or accumulation of body fat, including central obesity, dorsocervical fat enlargement (buffalo hump), peripheral wasting, facial wasting, breast enlargement, and general cushingoid appearance, has been reported in patients receiving PIs, including ritonavir.1 The mechanisms responsible for these adipogenic effects and the long-term consequences of these effects are unknown.1 A causal relationship has not been established.1

Patients with Hemophilia

Increased bleeding, including spontaneous skin hematomas and hemarthrosis, has been reported occasionally in patients with hemophilia A or hemophilia B receiving various PIs.1 While additional doses of antihemophilic factor were necessary to control bleeding episodes in some patients, PI therapy was continued or reintroduced in more than half of reported cases.1 A causal relationship to PI therapy has not been established.1

Resistance/Cross-resistance

Strains of HIV-1 with in vitro resistance to ritonavir have emerged during therapy with the drug.1 Varying degrees of cross-resistance can occur among the various PIs.1 Continued use of full-dose ritonavir therapy (600 mg twice daily) after loss of viral suppression may increase the likelihood of cross-resistance to other PIs.1

Laboratory Tests

Because ritonavir has been associated with alterations in certain laboratory test results (e.g., serum AST, ALT, GGT, CK, uric acid), appropriate clinical chemistry tests should be performed prior to and periodically after initiation of ritonavir therapy or whenever symptoms occur during therapy with the drug.1

Specific Populations

Pregnancy

There are no adequate and controlled studies to date using ritonavir in pregnant women, and the drugs should be used during pregnancy only when clearly needed.1

To monitor maternal-fetal outcomes of pregnant women exposed to antiretroviral agents, including ritonavir, an antiretroviral pregnancy registry was established.1 Clinicians are encouraged to contact the pregnancy registry at 800-258-4263 or [Web] to report cases of prenatal exposure to antiretroviral agents.1 The registry has received reports of 6100 cases of exposure to ritonavir-containing regimens (2800 first trimester exposures, over 3200 second and third trimester exposures). Data indicate that birth defects occurred in 2.3% of live births following first trimester exposures and in 2.9% of live births following second/third trimester exposures; the birth defect rate among pregnant women in the US reference population is 2.7%.1

Lactation

Limited data indicate that ritonavir is present in human milk.1 The effects of ritonavir on the breast-fed infant or on milk production are not known.1

The HHS perinatal HIV transmission guideline provides updated recommendations on infant feeding.202 The guideline states that patients with HIV should receive evidence-based, patient-centered counseling to support shared decision making about infant feeding.202 During counseling, patients should be informed that feeding with appropriate formula or pasteurized donor human milk from a milk bank eliminates the risk of postnatal HIV transmission to the infant.202 Additionally, achieving and maintaining viral suppression with antiretroviral therapy during pregnancy and postpartum reduces the risk of breastfeeding HIV transmission to <1%, but does not completely eliminate the risk.202 Replacement feeding with formula or banked pasteurized donor milk is recommended when patients with HIV are not on antiretroviral therapy and/or do not have a suppressed viral load during pregnancy (at a minimum throughout the third trimester), as well as at delivery.202

Females and Males of Reproductive Potential

There was no evidence that ritonavir affected fertility when the drug was given to male or female rats at exposure levels equivalent to 40 or 60%, respectively, of those expected with the usual human dosage.1 Higher ritonavir doses were not studied in these animals due to hepatic toxicity.1

Because ritonavir may reduce the efficacy of combined hormonal contraceptives, advise patients to use an effective alternative contraceptive method or an additional barrier method of contraception.1

Pediatric Use

Safety and efficacy of ritonavir have been established in pediatric patients older than 1 month of age.1

The antiviral activity of ritonavir in pediatric patients older than 1 month of age is similar to that reported in adult patients.1

Adverse effects reported to date in pediatric patients older than 1 month of age receiving ritonavir are similar to those reported in adults.1

Geriatric Use

Clinical studies of ritonavir to date have not included sufficient numbers of adults 65 years of age or older to determine whether geriatric patients respond differently than younger adults.1 In general, dosage for geriatric patients should be selected carefully, usually starting at the lower end of the dosing range, since these individuals frequently have decreased hepatic, renal, and/or cardiac function and concomitant disease and drug therapy.1

Hepatic Impairment

Because there have been reports of hepatic dysfunction, including fatal cases, in patients receiving ritonavir, the drug should be used with caution in patients with preexisting liver disease, liver enzyme abnormalities, or hepatitis, and consideration should be given to more frequent testing of serum AST and ALT concentrations in these patients, especially during the first 3 months of therapy.1 There may be an increased risk for transaminase elevations in patients with underlying hepatitis B or C.1

The dose-normalized steady-state exposure of ritonavir is similar in patients with mild hepatic impairment (Child-Pugh Class A) compared to patients with normal hepatic function.1 The dose-normalized steady-state exposure of ritonavir is approximately 40% lower in patients with moderate hepatic impairment (Child-Pugh Class B) compared to patients with normal hepatic function.1 Monitor patient response carefully in those with moderate hepatic impairment.1

Pharmacokinetic and safety data are not available in severe hepatic impairment (Child-Pugh Class C).1 Ritonavir is not recommended for use in patients with severe hepatic impairment.1

Renal Impairment

Pharmacokinetic data are not available in patients with renal impairment.1 Since renal excretion of ritonavir is negligible, reduced clearance in patients with renal impairment is not expected.1

Common Adverse Effects

The most frequent adverse reactions occurring in 25% or more of patients receiving ritonavir alone or with other antiretrovirals include GI reactions (e.g., diarrhea, nausea, vomiting, upper and lower abdominal pain), neurologic disturbances (including paresthesia and oral paresthesia), rash, and fatigue/asthenia.1

In vitro, ritonavir is metabolized principally by cytochrome P-450 (CYP) isoenzyme 3A, and to a lesser extent, CYP2D6.1 Ritonavir is a strong inhibitor of CYP3A.1 Ritonavir appears to induce CYP3A, 1A2, 2C9, 2C19, 2B6, and increases the activity of other enzymes, including glucuronosyl transferase.1

When ritonavir is used concomitantly with other protease inhibitors (i.e., atazanavir, darunavir, fosamprenavir), consult the prescribing information for that protease inhibitor, including important drug interaction information.1

Drugs Affecting Hepatic Microsomal Enzymes

Metabolism of ritonavir is mediated by CYP3A and CYP2D6, and concomitant use with drugs that induce these isoenzymes may result in clinically important decreases in ritonavir plasma concentrations.1 Concomitant use of ritonavir is contraindicated with drugs that are potent CYP3A inducers where significantly reduced ritonavir plasma concentrations may be associated with a potential loss of virologic response, and possible development of resistance and cross-resistance (e.g., apalutamide, St. John's wort [ Hypericum perforatum ]).1

Conversely, concomitant use of ritonavir with drugs that inhibit CYP3A and CYP2D6 isoenzymes may result in increased plasma ritonavir concentrations.1

The manufacturer's labeling and/or specialized references should be consulted for additional information and specific recommendations concerning therapeutic drug monitoring and dosage adjustments.1

Drugs Metabolized by Hepatic Microsomal Enzymes

Concomitant use of ritonavir with drugs primarily metabolized by CYP3A may increase plasma concentrations of the substrate.1 Drugs highly dependent on CYP3A metabolism with high first-pass metabolism appear to be the most susceptible to large increases in AUC.1 Ritonavir is contraindicated for concomitant use with drugs highly dependent on CYP3A for clearance and for which elevated plasma concentrations are associated with serious and/or life-threatening events (e.g., alfuzosin, amiodarone, cisapride, colchicine [in patients with renal or hepatic impairment], dronedarone, ergot alkaloids, flecainide, lomitapide, lovastatin, lurasidone, oral midazolam, pimozide, propafenone, quinidine, ranolazine, sildenafil used for treatment of PAH, simvastatin, triazolam, voriconazole).1 Concomitant use of ritonavir with other CYP3A substrates may require a dosage adjustment and additional monitoring.1

Concomitant use of ritonavir with substrates of CYP2D6 could result in up to twofold increases in the AUC of the substrate, which may require proportional dosage adjustments.1

The manufacturer's labeling and/or specialized references should be consulted for additional information and specific recommendations concerning therapeutic drug monitoring and dosage adjustments.1

Alfuzosin

Concomitant use of ritonavir and alfuzosin is contraindicated.1 Concomitant use of the drugs may result in increased plasma concentrations of alfuzosin and hypotension.1

Anticancer Agents

Abemaciclib

Concomitant use of abemaciclib and ritonavir may result in increased abemaciclib concentrations.1

Apalutamide

Concomitant use of apalutamide and ritonavir may result in increased apalutamide concentrations and reduced ritonavir concentrations.1 Concomitant use of apalutamide and ritonavir is contraindicated due to the potential loss of virologic response to ritonavir and the potential development of resistance to other PIs.1

Dasatinib

Concomitant use of dasatinib and ritonavir may result in increased dasatinib concentrations; dosage of the antineoplastic agent may need to be decreased or the dosing interval adjusted.1 Consult the prescribing information for dasatinib for dosage recommendations on concomitant use with strong CYP3A inhibitors such as ritonavir.1

Encorafenib

Concomitant use of encorafenib and ritonavir may result in increased encorafenib concentrations.1 Concomitant use of encorafenib and ritonavir is not recommended due to the potential for serious adverse events such as QT prolongation.1 If the concomitant use of encorafenib and ritonavir cannot be avoided, consult encorafenib prescribing information for dosage modification of encorafenib.1

Fostamatinib

Concomitant use of fostamatinib and ritonavir may result in increased concentrations of R406 (fostamatinib metabolite) and increases in dose-related adverse events (e.g., hepatoxicity, neutropenia).1 If fostamatinib and ritonavir are used concomitantly, monitor for toxicities from increased exposure (e.g., hepatotoxicity, neutropenia); a reduced dosage of fostamatinib may be necessary.1

Ibrutinib

Concomitant use of ibrutinib and ritonavir may cause increased ibrutinib concentrations.1 Avoid concomitant use of ibrutinib and ritonavir.1

Ivosidenib

Concomitant use of ivosidenib and ritonavir may result in increased ivosidenib concentrations.1 Concomitant use of ivosidenib and ritonavir is not recommended due to the potential for serious adverse events such as QT prolongation1 If concomitant use cannot be avoided, reduce the ivosidenib dosage to 250 mg once daily.1

Neratinib

Concomitant use of neratinib and ritonavir may result in increased neratinib concentrations.1 Avoid concomitant use of neratinib and ritonavir.1

Nilotinib

Concomitant use of nilotinib and ritonavir may result in increased nilotinib concentrations; dosage of the antineoplastic agent may need to be decreased or the dosing interval adjusted.1 Consult the prescribing information for nilotinib for dosage recommendations on concomitant use with strong CYP3A inhibitors such as ritonavir.1

Venetoclax

Concomitant use of venetoclax and ritonavir may result in increased venetoclax concentrations.1 Avoid concomitant use of venetoclax and ritonavir.1

Vinca Alkaloids

Concomitant use of vincristine or vinblastine and ritonavir may result in increased concentrations of the vinca alkaloid.1 The manufacturer of ritonavir states that temporarily withholding ritonavir-containing antiretroviral regimens should be considered in patients who develop substantial hematologic or GI toxicity from the vinca alkaloid.1 Alternatively, use of an antiretroviral regimen that does not include agents that inhibit CYP3A or the P-glycoprotein transport system should be considered.1

Anticoagulants

Rivaroxaban

Concomitant use of rivaroxaban (single 10-mg dose on days 0 and 7) and full-dose ritonavir (600 mg twice daily on days 2-7) resulted in a 60% increase in peak plasma concentrations of rivaroxaban and a 150% increase in the area under the concentration-time curve (AUC) of the drug.1 Increased rivaroxaban concentrations may lead to increased risk of bleeding.1

Concomitant use of rivaroxaban and ritonavir should be avoided.1

Warfarin

Concomitant use of ritonavir and warfarin may result in decreased plasma concentrations of R -warfarin and increased or decreased plasma concentrations of S -warfarin.1 If ritonavir and warfarin are used concomitantly, frequent initial monitoring of the INR is recommended.1

Antifungal Agents

Fluconazole

In a multiple-dose cross-over study in a limited number of healthy adults, concomitant use of fluconazole (400 mg on day 1, then 200 mg daily for 4 days) and ritonavir (200 mg every 6 hours for 4 days) increased the mean peak plasma concentration and AUC of ritonavir by 15% or less.1

Itraconazole

Concomitant use of ritonavir and itraconazole may increase plasma concentrations of both drugs.1 Itraconazole dosage should not exceed 200 mg daily in patients receiving ritonavir.1

Ketoconazole

Concomitant use of ketoconazole (200 mg daily for 7 days) and full-dose ritonavir (500 mg every 12 hours for 10 days) increased the peak plasma concentration and AUC of ritonavir by 10 or 18%, respectively, and increased the peak plasma concentration and AUC of ketoconazole by 55 and about 300%, respectively.1 Ketoconazole dosage should not exceed 200 mg daily in patients receiving ritonavir.1

Voriconazole

Concomitant use of ritonavir (400 mg twice daily) and voriconazole decreases the AUC and peak plasma concentration of voriconazole by 82 and 66%, respectively.1 Concomitant use of ritonavir at dosages of 400 mg every 12 hours or greater with voriconazole is contraindicated due to the potential loss of antifungal response.1 Concomitant use of ritonavir 100 mg and voriconazole is not recommended unless benefits outweigh risks.1

Antimalarial and Antiprotozoal Agents

Concomitant use of ritonavir and quinine is predicted to result in increased plasma concentrations of quinine; dosage reduction of the antimalarial agent may be necessary.1

Concomitant use of atovaquone and ritonavir is predicted to result in decreased plasma concentrations of the antiprotozoal agent.1 Although the clinical importance of the interaction is unknown, atovaquone dosage may need to be increased.1

Antimycobacterial Agents

Bedaquiline

Concomitant use of ritonavir and bedaquiline is predicted to result in increased plasma concentrations of bedaquiline.1 Concomitant use of ritonavir and bedaquiline is not recommended unless benefits outweigh risks.1

Rifabutin

Concomitant use of ritonavir and rifabutin results in substantially increased plasma concentrations of rifabutin and its 25- O -desacetyl metabolite.1 In a limited number of healthy individuals, concomitant use of rifabutin (150 mg once daily for 14 days) and full-dose ritonavir (500 mg every 12 hours for 10 days) increased peak concentrations of rifabutin and its 25- O -desacetyl metabolite by 2.5- and 16-fold, respectively, and increased their AUCs by 4- and 38-fold, respectively.1

If ritonavir is used concomitantly with rifabutin, the rifabutin dosage should be decreased to 150 mg every other day or 3 times weekly (further dosage reduction may be needed).1

Rifampin

Rifampin increases the activity of CYP3A isoenzymes and increases clearance of ritonavir resulting in decreased plasma concentrations of the PI.1 Preliminary data from a study evaluating concomitant use of rifampin (300 or 600 mg daily for 10 days) and full-dose ritonavir (500 mg every 12 hours for 20 days) in healthy adults indicate that the peak plasma concentrations of ritonavir are decreased by 25% and the AUC of the drug is decreased by 35%.1

Because of the possibility of loss of virologic response, concomitant use of rifampin and full-dose ritonavir or ritonavir-boosted PIs is not recommended; use of other antimycobacterial agents (e.g., rifabutin) should be considered.1

Antiretroviral Agents

HIV Entry and Fusion Inhibitors

Maraviroc

Concomitant use of maraviroc with ritonavir may result in increased maraviroc concentrations.1 Consult maraviroc prescribing information on the concomitant use of ritonavir and ritonavir-boosted PIs.1

HIV Integrase Inhibitors (INSTIs)

Raltegravir

Concomitant use of raltegravir (single 400-mg dose) and low-dose ritonavir (100 mg twice daily) decreases the peak plasma concentration and AUC of raltegravir by 24 and 16%, respectively.1

Although data are not available regarding concomitant use of raltegravir and ritonavir dosage exceeding 100 mg twice daily, decreased raltegravir concentrations may occur.1

HIV Nonnucleoside Reverse Transcriptase Inhibitors (NNRTIs)

Delavirdine

Concomitant use of delavirdine and ritonavir may result in increased ritonavir concentrations.1 Appropriate dosages for concomitant use of delavirdine and ritonavir with respect to safety and efficacy have not been established.1

HIV Nucleoside Reverse Transcriptase Inhibitors (NRTIs)

In vitro tests in MT-4 cells (a human lymphoblastoid T-cell line) indicate that ritonavir may potentiate the antiretroviral activity of zidovudine and didanosine against HIV-1.1

Didanosine

Concomitant use of full-dose oral ritonavir (600 mg every 12 hours) with oral didanosine (200 mg every 12 hours) for 4 days decreased peak plasma concentrations and AUC of didanosine by 13-16%.1 Concomitant use of ritonavir and didanosine does not appear to result in a clinically important effect on the pharmacokinetics of ritonavir.1

Zidovudine

Concomitant use of full-dose oral ritonavir ( 300 mg every 6 hours) with oral zidovudine (200 mg every 8 hours) for 4 days decreased peak plasma concentrations and AUC of zidovudine by 25-27%.1 Concomitant use of ritonavir and zidovudine does not appear to result in clinically important effects on the pharmacokinetics of ritonavir.1

HIV Protease Inhibitors (PIs)

For information on dosage adjustments of protease inhibitors when low-dose ritonavir is used concomitantly as a pharmacokinetic enhancer for therapeutic advantage ( ritonavir-boosted therapy), see the prescribing information for the specific HIV protease inhibitor.1

Atazanavir

Concomitant use of ritonavir and atazanavir may result in substantially increased plasma concentrations of atazanavir.1 Dosage reduction of ritonavir is necessary when used concomitantly with atazanavir.1 Consult the atazanavir prescribing information for recommendations on concomitant use with ritonavir.1

Because the impact on the PR interval has not been evaluated during concomitant use of ritonavir and atazanavir, the drugs should be used concomitantly with caution and clinical monitoring.1

Darunavir

Concomitant use of ritonavir and darunavir results in substantially increased plasma concentrations of darunavir.1 Dosage reduction of ritonavir is necessary when used concomitantly with darunavir.1 Consult the darunavir prescribing information for recommendations on concomitant use with ritonavir.1

Fosamprenavir

Concomitant use of ritonavir and fosamprenavir may result in substantially increased plasma concentrations of amprenavir.1 Dosage reduction of ritonavir is necessary when used concomitantly with fosamprenavir.1 Consult the fosamprenavir prescribing information for recommendations on concomitant use with ritonavir.1

Bosentan

Concomitant use of bosentan and ritonavir may result in increased bosentan concentrations.1

In patients who have been receiving ritonavir for at least 10 days, bosentan should be initiated using a dosage of 62.5 mg once daily or every other day based on individual tolerability.1

In patients who have been receiving bosentan, bosentan should be discontinued for at least 36 hours prior to initiating ritonavir; after at least 10 days of PI therapy, bosentan can be resumed using a dosage of 62.5 mg once daily or every other day based on individual tolerability.1

Cardiovascular Agents

Antiarrhythmics

Concomitant use of ritonavir and amiodarone, dronedarone, flecainide, propafenone, or quinidine is contraindicated since ritonavir is expected to produce substantially increased plasma concentrations of these cardiac drugs and increase the potential for serious and/or life-threatening adverse effects associated with the drugs such as cardiac arrhythmias.1

Concomitant use of ritonavir and disopyramide, mexiletine, or systemic lidocaine is predicted to result in an increase in plasma concentrations of these agents.1 Caution is advised if ritonavir is administered with these agents; plasma concentrations of the cardiovascular agent should be monitored.1 There have been postmarketing reports of cardiac and neurologic events when ritonavir was used concomitantly with disopyramide or mexiletine, and the possibility of a drug interaction cannot be excluded.1

Beta-Blockers

Concomitant use of ritonavir and metoprolol or timolol is predicted to result in an increase in plasma concentrations of the β-adrenergic blocking agent.1 Caution is advised if ritonavir is administered with these agents; dosage reduction of the β-adrenergic blocking agent may be necessary.1 Careful monitoring of the patient is recommended.1 There have been postmarketing reports of cardiac and neurologic events when ritonavir was used concomitantly with β-adrenergic blocking agents, and the possibility of a drug interaction cannot be excluded.1

Because the impact on the PR interval has not been evaluated during concomitant use of ritonavir and β-adrenergic blocking agents, the drugs should be used concomitantly with caution and clinical monitoring.1

Calcium-Channel Blocking Agents

Concomitant use of ritonavir and calcium-channel blocking agents such as diltiazem, nifedipine, or verapamil is predicted to result in an increase in plasma concentrations of these agents.1 Caution is advised if ritonavir is administered with these agents; dosage reduction of the calcium-channel blocking agent may be necessary.1 Careful monitoring of the patient is recommended.1

Digoxin

Caution is advised if ritonavir and digoxin are used concomitantly.1 Serum digoxin concentrations should be monitored as appropriate.1

Because the impact on the PR interval has not been evaluated during concomitant use of ritonavir and digoxin, the drugs should be used concomitantly with caution and clinical monitoring.1

Lipid-Modifying Agents

Concomitant use of some hydroxymethylglutaryl-CoA (HMG-CoA) reductase inhibitors (statins) (e.g., atorvastatin, lovastatin) and PIs, including ritonavir, may increase plasma concentrations of these antilipemic agents resulting in increased effects and increased risk of statin-associated adverse effects, including myopathy and rhabdomyolysis.1

Atorvastatin

When atorvastatin is used concomitantly with ritonavir, the dosage should be carefully titrated and the lowest necessary dosage used.1 If atorvastatin is used concomitantly with a ritonavir-boosted PI regimen, the prescribing information for the PI should be consulted for recommendations.1

Lomitapide

Concomitant use of lomitapide and ritonavir is expected to increase concentrations of lomitapide.1 Because lomitapide is a sensitive substrate of CYP3A, use with CYP3A inhibitors can increase the exposure up to 27-fold.1 Concomitant use of lomitapide with moderate or strong CYP3A inhibitors, such as ritonavir, is contraindicated .1

Lovastatin

Concomitant use of lovastatin and ritonavir is contraindicated .1

Rosuvastatin

When rosuvastatin is used concomitantly with ritonavir, the dosage should be carefully titrated and the lowest necessary dosage used.1 If rosuvastatin is used concomitantly with a ritonavir-boosted protease inhibitor regimen, the prescribing information for the protease inhibitor should be consulted for recommendations.1

Simvastatin

Concomitant use of simvastatin and ritonavir is contraindicated .1

CNS Agents

Anticonvulsants

Because anticonvulsants have a narrow therapeutic margin, drug concentrations should be monitored and/or monitoring for therapeutic and adverse effects should be increased in patients receiving ritonavir concomitantly.1

Carbamazepine, Clonazepam, Ethosuximide

Concomitant use of ritonavir and carbamazepine, clonazepam, or ethosuximide is predicted to increase plasma concentrations of the anticonvulsant.1 Caution is advised if ritonavir is administered with these agents; dosage reduction of the anticonvulsant may be necessary.1 Clinicians should consider monitoring concentrations of the anticonvulsant.1

Divalproex, Lamotrigine, Phenytoin

Concomitant use of ritonavir and divalproex, lamotrigine, or phenytoin is predicted to result in a decrease in plasma concentrations of the anticonvulsant.1 Caution is advised if ritonavir is administered with these agents; dosage increase of the anticonvulsant may be necessary.1 Clinicians should consider monitoring concentrations of the anticonvulsant.1

Antidepressants

Bupropion

Concomitant use of ritonavir with bupropion may reduce plasma concentrations of bupropion and hydroxybupropion (active metabolite); patients should be monitored for response to bupropion.1

Nefazodone

Concomitant use of ritonavir with nefazodone increases or is predicted to increase plasma concentrations of nefazodone.1 Caution is advised if ritonavir is administered with nefazodone; dosage reduction of nefazodone may be necessary.1

There have been postmarketing reports of cardiac and neurologic events when ritonavir was used concomitantly with nefazodone, and the possibility of a drug interaction cannot be excluded.1

Selective Serotonin-reuptake Inhibitors

Concomitant use of ritonavir with some selective serotonin uptake inhibitors (SSRIs) (e.g., fluoxetine, paroxetine) may increase plasma concentrations of the SSRI.1 Caution is advised if ritonavir is administered with SSRIs; dosage of the SSRI may need to be reduced.1

In one study in healthy individuals receiving fluoxetine (30 mg every 12 hours for 8 days), administration of a single dose of ritonavir (600 mg) resulted in a 19% increase in the AUC of ritonavir but had no effect on the peak plasma concentration of the drug.1 Adverse cardiac and neurologic effects have been reported in patients receiving ritonavir and fluoxetine concomitantly, and the possibility of a drug interaction cannot be excluded.1

Trazodone

Concomitant use of ritonavir with trazodone increases or is predicted to increase plasma concentrations of trazodone.1 Caution is advised if ritonavir is administered with trazodone; dosage reduction of trazodone may be necessary.1 Nausea, dizziness, hypotension, and syncope were observed when ritonavir and trazodone were used concomitantly.1

Administration of a single 50-mg dose of trazodone with ritonavir (200 mg every 12 hours) for 4 doses resulted in a 2.4-fold increase in the AUC of trazodone and a 34% increase in the peak plasma concentration of trazodone.1

Tricyclic Antidepressants

Concomitant use of ritonavir with some tricyclic antidepressants (e.g., amitriptyline, desipramine, nortriptyline) is expected to increase plasma concentrations of the antidepressant.1 Reduction of the antidepressant dosage may be required.1

Clinically important increases in plasma desipramine concentrations may occur in patients receiving ritonavir, and the manufacturer of ritonavir recommends that reduction of the usual desipramine dosage be considered and plasma desipramine concentrations be monitored if the drugs are used concomitantly.1 Administration of a single 100-mg dose of desipramine in a limited number of healthy individuals receiving full-dose ritonavir (500 mg every 12 hours for 12 days) resulted in a 22% increase in peak desipramine plasma concentrations and a 145% increase in the AUC of the drug; plasma concentrations and AUC of 2-OH desipramine were decreased 67 and 15%, respectively.1

Antipsychotics

Lurasidone

Concomitant use of ritonavir and lurasidone is contraindicated because ritonavir is expected to produce substantially increased concentrations of lurasidone and increase the potential for serious and/or life-threatening adverse reactions.1

Perphenazine, Risperidone, Thioridazine

Concomitant use of ritonavir with antipsychotic agents (e.g., perphenazine, risperidone, thioridazine) increases or is predicted to increase plasma concentrations of these agents.1

Dosage reduction of the antipsychotic agent may be necessary.1

Pimozide

Concomitant use of ritonavir and pimozide is contraindicated since ritonavir is expected to produce substantially increased plasma concentrations of pimozide and increase the potential for serious and/or life-threatening adverse effects associated with the drug such as cardiac arrhythmias.1

Quetiapine

Concomitant use of quetiapine and ritonavir is expected to result in increased quetiapine concentrations.1 In patients already receiving ritonavir, refer to the quetiapine prescribing information for initial dosing and titration recommendations of the antipsychotic.1 If ritonavir is initiated in a patient receiving a stable dosage of quetiapine, dosage of quetiapine should be reduced to one-sixth of the original dosage and the patient should be monitored for adverse effects of the antipsychotic.1 Refer to quetiapine prescribing information for monitoring recommendations for adverse effects1 .

CNS Stimulants

Methamphetamine

Concomitant use with ritonavir is predicted to result in an increase in plasma concentrations of methamphetamine.1 Caution is advised if ritonavir is administered with methamphetamine; dosage reduction of methamphetamine may be necessary.1

Opiate Agonists

Fentanyl

Concomitant use of fentanyl and ritonavir is expected to increase fentanyl plasma concentrations.1 If fentanyl and ritonavir are used concomitantly, patients should be carefully monitored for therapeutic and adverse effects, including potentially fatal respiratory depression.1

Meperidine

Administration of a single 50-mg oral dose of meperidine and full-dose ritonavir (500 mg every 12 hours for 10 days) decreased the AUC of meperidine by 62% and increased the AUC of its metabolite, normeperidine, by 47%.1

The manufacturer of ritonavir does not recommend increasing meperidine dosage or long-term concomitant use of meperidine and ritonavir since such dosage adjustments or use may result in increased concentrations of normeperidine, which has analgesic and CNS-stimulant activity (e.g., seizures).1

Methadone

Administration of a single 5-mg dose of methadone and full-dose ritonavir (500 mg every 12 hours for 15 days) decreased the AUC of methadone by 36%.1

Individuals receiving concomitant ritonavir and methadone therapy should be informed of this potential interaction, and should be closely monitored for manifestations of opiate withdrawal when ritonavir therapy is initiated; an increase in the maintenance dosage of methadone may be necessary.1

Tramadol

Caution is advised if ritonavir is administered with tramadol; dosage reduction of the analgesic may be necessary.1

Sedatives and Hypnotics

Alprazolam

In one study, concomitant use of full-dose ritonavir (500 mg every 12 hours for 10 days) with a single 1-mg oral dose of alprazolam decreased the peak plasma concentration and AUC of alprazolam by 16 and 12%, respectively.1

Buspirone

Concomitant use of ritonavir with buspirone is predicted to increase the plasma concentrations of buspirone.1 Caution is advised if ritonavir used concomitantly; dosage reduction of buspirone may be necessary.1

Clorazepate, Diazepam, Estazolam, Flurazepam

Concomitant use of ritonavir with clorazepate, diazepam, estazolam, or flurazepam is predicted to increase plasma concentrations of the benzodiazepine.1 Dosage reduction of the benzodiazepine may be necessary.1

Midazolam, Triazolam

Concomitant use of ritonavir and oral midazolam or triazolam is contraindicated since ritonavir is expected to produce substantially increased plasma concentrations of these sedative-hypnotics and increase the potential for serious and/or life-threatening adverse effects associated with the drugs (e.g., prolonged or increased sedation or respiratory depression).1

If ritonavir is used concomitantly with parenteral midazolam, the manufacturer of ritonavir states that patients should be monitored closely for respiratory depression and/or prolonged sedation and reduced dosage of midazolam should be considered, particularly if multiple parenteral doses are administered.1

Zolpidem

Concomitant use of ritonavir with zolpidem is predicted to increase plasma concentrations of zolpidem.1 Dosage reduction of zolpidem may be necessary if used concomitantly with ritonavir.1

Colchicine

Concomitant use of PIs, including ritonavir, and colchicine may result in increased plasma concentrations of colchicine.1 Concomitant use of colchicine and ritonavir is contraindicated in patients with renal and/or hepatic impairment due to the increased risk of serious and life-threatening adverse reactions.1 If used concurrently in patients with normal renal and hepatic function, colchicine dosage adjustments are recommended.1

When colchicine is used for treatment of gout flares in patients with normal renal or hepatic function who are receiving ritonavir, the manufacturer of ritonavir recommends that an initial colchicine dose of 0.6 mg be followed by 0.3 mg 1 hour later and that the dose be repeated no earlier than 3 days later.1

When colchicine is used for prophylaxis of gout flares in patients with normal renal or hepatic function receiving ritonavir, the manufacturer of ritonavir recommends that the colchicine dosage be reduced to 0.3 mg once daily in those originally receiving 0.6 mg twice daily or decreased to 0.3 mg once every other day in those originally receiving 0.6 mg once daily.1

When colchicine is used for treatment of familial Mediterranean fever (FMF) in patients with normal renal or hepatic function receiving ritonavir, the manufacturer of ritonavir recommends that a maximum colchicine dosage of 0.6 mg daily (may be given as 0.3 mg twice daily) be used.1

Corticosteroids

Concomitant use of systemic, inhaled, intranasal, and ophthalmic corticosteroids whose pharmacokinetics are significantly affected by strong CYP3A inhibitors (e.g., betamethasone, budesonide, ciclesonide, dexamethasone, fluticasone, methylprednisolone, mometasone, prednisone, triamcinolone) such as ritonavir may significantly increase exposure to the corticosteroid and increase the risk of Cushing's syndrome and adrenal suppression.1 Consider use of a corticosteroid whose exposure is less affected by strong CYP3A inhibitors (e.g., beclomethasone, prednisolone), especially when expected use of the corticosteroid is long-term.1

Administration of fluticasone propionate nasal spray (200 mcg once daily) with low-dose ritonavir (100 mg every 12 hours) for 7 days resulted in approximately 350-fold and 25-fold increases in the AUC and peak plasma concentrations of fluticasone, respectively; the plasma cortisol AUC was also significantly decreased by 86%.1

Co-trimoxazole

Administration of a single dose of co-trimoxazole (sulfamethoxazole 800 mg and trimethoprim 160 mg) in healthy individuals receiving full-dose ritonavir (500 mg every 12 hours for 12 days) decreased the AUC of sulfamethoxazole by 20% and increased the AUC of trimethoprim by 20%.1

Elagolix

Concomitant use of elagolix with ritonavir may result in increased elagolix concentrations and decreased ritonavir concentrations.1 Concomitant use of elagolix (200 mg twice daily) and ritonavir for greater than 1 month is not recommended due to a possible risk of adverse events (i.e., bone loss, hepatic transaminase elevations).1 Concomitant use of elagolix (150 mg once daily) and ritonavir should not exceed 6 months' duration.1

Ergot Alkaloids

Concomitant use of ritonavir and ergot alkaloids (dihydroergotamine, ergotamine, methylergonovine) is contraindicated since ritonavir is expected to produce substantially increased plasma concentrations of these ergot alkaloids and increase the potential for serious and/or life-threatening adverse effects associated with the drugs such as ergot toxicity.1 There have been postmarketing reports of acute ergot toxicity characterized by peripheral vasospasm and ischemia of the extremities in patients who received ritonavir concomitantly with ergotamine or dihydroergotamine1 .

Estrogens

Concomitant use of ethinyl estradiol (oral or transdermal preparations) and ritonavir may result in substantially decreased plasma concentrations of ethinyl estradiol.1 In a study evaluating administration of a single dose of an oral contraceptive containing ethinyl estradiol (50-mcg of ethinyl estradiol) in healthy women receiving full-dose ritonavir (500 mg every 12 hours for 16 days), peak plasma concentrations and AUC of the estrogen were decreased 32% and 40%, respectively.1

The manufacturer of ritonavir recommends use of alternative methods of contraception in patients receiving ritonavir.1

GI Drugs

Cisapride

Concomitant use of ritonavir and cisapride is contraindicated since ritonavir is expected to produce substantially increased plasma concentrations of unchanged cisapride and increase the potential for serious and/or life-threatening adverse effects associated with the drug such as cardiac arrhythmias.1

Dronabinol

Concomitant use of ritonavir and dronabinol is predicted to result in increased plasma concentrations of the antiemetic.1 Caution is advised and a reduction in the dronabinol dosage may be necessary if ritonavir and dronabinol are used concomitantly.1

HCV Protease Inhibitors

Glecaprevir/Pibrentasvir

Concomitant use of glecaprevir/pibrentasvir with ritonavir is not recommended due to increased plasma concentrations of glecaprevir and pibrentasvir.1

Immunosuppressive Agents

Concomitant use of ritonavir with cyclosporine, sirolimus, or tacrolimus is predicted to result in increased plasma concentrations of the immunosuppressive agent.1 Clinicians should monitor plasma concentrations of the immunosuppressive agent.1

Macrolides

Concomitant use of ritonavir and clarithromycin may affect plasma concentrations of both drugs.1 In one study in healthy individuals, concomitant use of ritonavir (200 mg every 8 hours) with clarithromycin (500 mg every 12 hours) for 4 days increased the peak plasma concentration and AUC of clarithromycin by 31 and 77%, respectively, and decreased the peak plasma concentration and AUC of 14-hydroxyclarithromycin by 99 and 100%, respectively.1 In this study, the peak plasma concentration and AUC of ritonavir were increased 15 and 12%, respectively.1

The manufacturer of ritonavir states that modification of the usual clarithromycin dosage generally is not necessary in those with normal renal function; however, the clarithromycin dose should be reduced by 50% in patients with creatinine clearances of 30-60 mL/minute and reduced by 75% in patients with creatinine clearances less than 30 mL/minute.1

Phosphodiesterase Type 5 Inhibitors

Avanafil

Concomitant use of full-dose ritonavir (600 mg twice daily) and avanafil (single 50-mg dose) results in an approximately 13-fold increase in the AUC of avanafil.1 Avanafil should not be used in patients receiving ritonavir; a safe and effective dosage of avanafil has not been established for such patients.1

Sildenafil

Concomitant use of full-dose ritonavir (500 mg twice daily) and sildenafil (single 100-mg dose) results in an approximately 11-fold increase in the AUC of sildenafil.1

If sildenafil (Revatio^®) is used for the treatment of pulmonary arterial hypertension (PAH), concomitant use of ritonavir is contraindicated due to the potential for adverse events associated with sildenafil (e.g., visual abnormalities, hypotension, prolonged erection, and syncope).1

If sildenafil is used for the treatment of erectile dysfunction in a patient receiving ritonavir, the sildenafil dosage should not exceed 25 mg in 48 hours; the patient should be monitored for sildenafil-related adverse effects.1

Tadalafil

Concomitant use of ritonavir with tadalafil results in a 124% increase in the AUC of tadalafil.1

If tadalafil (Adcirca^®) is initiated for the treatment of PAH in patients who have been receiving ritonavir for at least 1 week, an initial tadalafil dosage of 20 mg once daily is recommended; dosage may be increased to 40 mg once daily based on individual tolerability.1 Use of tadalafil (Adcirca^®) for the treatment of PAH should be avoided during initiation of PI therapy.1 If ritonavir is indicated in a patient already receiving tadalafil (Adcirca^®) for the treatment of PAH, tadalafil should be discontinued for at least 24 hours before starting ritonavir; tadalafil can be restarted after at least 1 week of ritonavir therapy using an initial tadalafil dosage of 20 mg once daily and increasing the dosage to 40 mg once daily based on individual tolerability.1

If tadalafil is used for the treatment of erectile dysfunction in a patient receiving ritonavir, the dosage of tadalafil should not exceed 10 mg every 72 hours; the patient should be monitored for tadalafil-related adverse effects.1

Vardenafil

Concomitant use of ritonavir with vardenafil results in a 49-fold increase in the AUC of vardenafil.1

If vardenafil is used for the treatment of erectile dysfunction in a patient receiving ritonavir, the dosage of vardenafil should not exceed 2.5 mg in 72 hours; the patient should be monitored for adverse effects related to vardenafil.1

Ranolazine

Concomitant use of ranolazine and ritonavir is contraindicated since use is expected to result in increased concentrations of ranolazine that may result in serious and/or life-threatening reactions.1

Salmeterol

Concomitant use of salmeterol and ritonavir results in increased salmeterol concentrations and may result in an increased risk of salmeterol-associated adverse cardiovascular effects, including QT interval prolongation, palpitations, and sinus tachycardia.1 The manufacturer of ritonavir states that concomitant use of ritonavir and salmeterol is not recommended.1

St. John's Wort ( Hypericum perforatum )

Concomitant use of St. John's wort (Hypericum perforatum) and ritonavir is contraindicated since such use is expected to result in suboptimal antiretroviral concentrations and may be associated with loss of virologic response and development of resistance.1

Theophylline

Concomitant use of theophylline and ritonavir may result in decreased concentrations of theophylline, and the manufacturer of ritonavir states that theophylline dosage may need to be increased and therapeutic monitoring should be considered if ritonavir is initiated in patients receiving theophylline therapy.1 In a limited number of individuals receiving theophylline (3 mg/kg every 8 hours for 15 days), concomitant use of full-dose ritonavir (500 mg every 12 hours for 10 days) decreased theophylline peak plasma concentrations and AUC by 32 and 43%, respectively.1

Description

Ritonavir inhibits replication of retroviruses by interfering with HIV protease.1 The drug, therefore, exerts an effect against retroviruses by acting as an HIV protease inhibitor (PI).1 Through inhibition of HIV protease, processing of the Gag-Pol polyprotein precursor does not occur, which results in the production of immature, noninfectious HIV.1

The pharmacokinetics of ritonavir have been studied in healthy adults and in adults with human immunodeficiency virus (HIV) infection.1 Pharmacokinetic studies have not revealed gender-related or race-related differences in the pharmacokinetics of ritonavir.1 In addition, there has been no evidence of age-related differences in the pharmacokinetics of the drug in adults 18-63 years of age.1 Pharmacokinetics of the drug have been evaluated in a limited number of HIV-infected children 1 month of age or older.1 The pharmacokinetics of ritonavir in adults older than 63 years of age and in individuals with renal impairment have not been determined to date.1

Ritonavir is well absorbed following oral administration, and peak plasma concentrations of the drug generally are attained within 2-4 hours.1 Following oral administration of a single 600-mg dose of radiolabeled ritonavir given as an oral solution, essentially all of the dose in systemic circulation represented unchanged ritonavir.1 Presence of food in the GI tract may affect the rate and/or extent of absorption of oral ritonavir; however, the effect that food has on GI absorption of ritonavir varies depending on the dosage form of the drug administered.1 Administration of ritonavir tablets, or oral powder with food generally decreases the rate and extent of absorption of the drug.1 Administration of a single 100-mg ritonavir tablet with a high-fat (917 kcal, 60% fat) or moderate-fat meal results in a 21-23% decrease in ritonavir AUC and peak plasma concentration.1 Following administration of a single 100-mg dose of the oral powder with a moderate-fat or high-fat meal, the AUC and peak plasma concentration are decreased by 23-49% relative to fasting conditions.1 Results of a limited study in HIV-infected children 2-14 years of age indicate that a ritonavir dosage of 350-400 mg/m² twice daily results in plasma concentrations that approximate those reported in adults receiving a ritonavir dosage of 600 mg (approximately 330 mg/m²) twice daily.1 In HIV-infected infants 1-24 months of age receiving a ritonavir dosage of 350-450 mg/m² twice daily, trough concentrations of ritonavir were lower than those reported in adults receiving a ritonavir dosage of 600 mg twice daily.1 Higher ritonavir exposures were not observed in infants receiving a ritonavir dosage of 450 mg/m² twice daily compared with those receiving a dosage of 350 mg/m² twice daily.1 Results of a study in a limited number of HIV-infected adults indicate that use of a ritonavir dosage of 400 mg twice daily in patients with mild hepatic impairment results in similar ritonavir exposures as those reported in control individuals receiving 500 mg twice daily.1 In a limited number of adults with moderate hepatic impairment, administration of ritonavir 400 mg twice daily resulted in dose-normalized steady-state ritonavir exposures approximately 40% lower than that reported in adults with normal hepatic function receiving ritonavir 500 mg twice daily.1 Ritonavir is 98-99% bound to plasma proteins, principally serum albumin and alpha-1 acid glycoprotein, over a concentration range of 0.01-30 mcg/mL.1 Mild or moderate hepatic impairment does not result in clinically important changes in protein binding of ritonavir.1 Limited data indicate that ritonavir is distributed into milk.1 The metabolic fate of ritonavir has not been fully determined, but the drug is metabolized in the liver.1 Systemic clearance averages 8.8 L/hr in patients receiving ritonavir 600 mg every 12 hours or 4.6 L/hr in those receiving a single 600-mg dose.1 Renal clearance has been reported to be less than 0.1 L/hr.1 The plasma half-life of ritonavir in adults averages 3-5 hours.1 Preliminary results of pharmacokinetic studies in HIV-infected children 1 month to 14 years of age indicate that ritonavir clearance at steady-state is 1.5—1.7 times greater in these children than in adults.1 Five ritonavir metabolites have been identified in human urine and feces.1 The isopropylthiazole oxidation metabolite (M2) appears to be the major metabolite.1 M2 (but not other metabolites) has antiviral activity similar to that of ritonavir; however, only very low concentrations of this metabolite are present in plasma.1 Results of in vitro studies using human liver microsomes indicate that metabolism of ritonavir is mediated by P-450 CYP3A isoenzymes and, to a lesser extent, by CYP2D6; both CYP3A and CYP2D6 contribute to the formation of M2.1 Ritonavir is excreted principally in the feces, both as unchanged drug and metabolites.1 Following oral administration of 600 mg of radiolabeled ritonavir as an oral solution, 86.4% of the dose is excreted in feces (33.8% as unchanged drug) and 11.3% of the dose is excreted in urine (3.5% as unchanged drug).1 Following continuous administration of ritonavir, plasma concentrations are lower than predicted from single-dose studies, presumably because of time- and dose-related increases in clearance.1 Because ritonavir is metabolized in the liver and is highly protein bound, it is unlikely that substantial amounts of the drug would be removed from the body by hemodialysis or peritoneal dialysis.1

Spectrum

Ritonavir is active in vitro against HIV-1.1 Ritonavir is active in vitro against strains of HIV-1 with in vitro resistance to zidovudine.1 The antiretroviral activity of ritonavir has been evaluated in vitro in various cell culture systems, including lymphoblastoid cell lines and peripheral blood lymphocytes.1 In vitro tests in MT-4 cells (a human lymphoblastoid T-cell line) indicate that ritonavir may potentiate the antiretroviral activity of zidovudine and didanosine against HIV-1.1 Depending on the cell culture system used, the EC₅₀ of ritonavir (concentration of the drug required to inhibit 50% of detectable HIV replication) for HIV-1 has ranged from 3.8-153 n M .1 The EC₅₀ of the drug for low passage clinical isolates averages 22 n M .1

Resistance

Ritonavir-resistant HIV-1 isolates have been detected in vitro and strains of HIV-1 with in vitro resistance to ritonavir have emerged during therapy with the drug.1 For information on genotypic assays used to detect specific HIV-1 genetic variants (mutations) and phenotypic assays used to measure HIV-1 drug resistance and recommendations regarding these assays, see In Vitro Resistance Testing under Guidelines for Use of Antiretroviral Agents: Laboratory Monitoring, in the Antiretroviral Agents General Statement 8:18.08.

Although the complete mechanism(s) of resistance or reduced susceptibility to ritonavir has not been fully determined to date, mutation of HIV protease appears to be a principal mechanism of resistance.1 Mutations that have been associated with decreased in vitro susceptibility to ritonavir include I84V, V82F, A71V, and M46I.1

Molecular analysis of ritonavir-resistant variants obtained from patients revealed a multistep process in which the initial amino acid substitutions principally occurred at positions V82A/F/T/S, I54V, A71V/T, and I36L, followed by M46I/L, K20R, I84V, L33F, and L90M.1 The V82A/F substitution appears to be necessary, but not sufficient, to confer phenotypic resistance (i.e., fivefold or greater decrease in susceptibility in vitro from baseline).1

Cross-Resistance

There is evidence from in vitro and in vivo studies that varying degrees of cross-resistance occurs among the various HIV PIs.1 In one study evaluating HIV-1 isolates obtained from patients receiving ritonavir therapy, all isolates had decreased susceptibility to ritonavir in vitro and some isolates had decreased susceptibility to indinavir in vitro; however, ritonavir-resistant strains remained susceptible to amprenavir and saquinavir.1

Cross-resistance between ritonavir and NRTIs or NNRTIs is highly unlikely since the drugs have different target enzymes.1

Advice to Patients

• Advise patients and/or caregivers to read and follow directions for preparation of ritonavir oral powder.1
• Advise caregivers to update their healthcare provider when their child's weight changes so that their ritonavir dose may be adjusted as necessary.1
• Critical nature of compliance with HIV therapy and importance of remaining under the care of a clinician.1 Stress importance of taking as prescribed; do not alter or discontinue antiretroviral regimen without consulting clinician.1
• Stress importance of using in conjunction with other antiretrovirals—not for monotherapy.1
• Stress importance of taking ritonavir with a meal.1,1
• If a dose is missed, it should be taken as soon as it is remembered and the next dose taken at the regularly scheduled time; if a dose is skipped, the next dose should not be doubled.1
• Advise patients that ECG changes (PR prolongation) have occurred; stress importance of consulting clinician if dizziness, lightheadedness, abnormal heart beats, or loss of consciousness occurs.1
• Inform patients that pre-existing liver disease, including hepatitis B virus (HBV) or hepatitis C virus (HCV) infections, can worsen during use of ritonavir, therefore, liver function test monitoring is necessary during therapy.1 Advise patients to inform their healthcare providers if signs and symptoms of worsening liver dysfunction develop (e.g., loss of appetite, stomach pain, jaundice, skin itchiness).1
• Advise patients to notify their healthcare provider if signs and symptoms suggestive of pancreatitis develop (e.g., nausea, vomiting, stomach pain).1
• Advise patients to inform their healthcare provider if a rash develops during treatment.1
• Inform patients that redistribution/accumulation of body fat may occur, with as yet unknown long-term health effects.1
• Inform patients that hyperglycemia, new-onset diabetes mellitus, or exacerbation of preexisting diabetes mellitus can occur.1 Patients should promptly notify their healthcare provider if signs and symptoms of diabetes develop (e.g., urinating frequently, excessive thirst or hunger, or excessive weight loss and/or increased blood glucose).1
• Inform patients that cholesterol and triglyceride levels may increase with use of ritonavir.1
• Inform patients with hemophilia that increased bleeding may occur when protease inhibitors such as ritonavir are used.1
• Advise patients to inform their clinician of existing or contemplated concomitant therapy, including prescription and OTC drugs and dietary or herbal supplements (e.g., St. John's Wort), as well as any concomitant illnesses.1
• Stress importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed.1 Inform patients that an antiretroviral pregnancy registry is available that monitors fetal outcomes of infants exposed to ritonavir.1 Providers can register patients by calling the Antiretroviral Pregnancy Registry (APR) at 1-800-258-4263.1 Inform patients using combined hormonal contraception to use an effective alternative contraceptive method or an additional barrier method during therapy with ritonavir because hormone levels may be decreased.1
• Inform patients of other important precautionary information.1

Only references cited for selected revisions after 1984 are available electronically.

1. AbbVie Inc. Norvir^®(ritonavir) tablets, oral solution, and oral powder prescribing information. North Chicago, IL; 2022 Dec.

77. Mueller BU, Nelson RP, Sleasman J et al. A phase I/II study of the protease inhibitor ritonavir in children with human immunodeficiency virus infection. Pediatrics . 1998; 101:335-43.

90. Abbott Laboratories, Abbott Park, IL: personal communication.

94. Nachman SA, Stanley K, Yogev R et al. Nucleoside analogs plus ritonavir in stable antiretroviral therapy-experienced HIV-infected children. JAMA . 2000; 283:492-8.

129. Cameron DW, Heath-Chiozzi M, Danner S et al for the Advanced HIV Disease Ritonavir Study Group. Randomised placebo-controlled trial of ritonavir in advanced HIV-1 disease. Lancet . 1998; 351:543-9.

183. Chadwick EG, Rodman JH, Britto P et al. Ritonavir-based highly active antiretroviral therapy in human immunodeficiency virus type 1-infected infants younger than 24 months of age. Pediatr Infect Dis . 2005; 24:793-800.

198. Centers for Disease Control and Prevention. Updated guidelines for antiretroviral postexposure prophylaxis after sexual, injection drug use, or other nonoccupational exposure to HIV - United States, 2016. From HHS AIDS Information (HIV.gov) website. http://clinicalinfo.hiv.gov/en/guidelines

199. Kuhar DT, Henderson DK, Struble KA et al. Updated US Public Health Service guidelines for the management of occupational exposures to human immunodeficiency virus and recommendations for postexposure prophylaxis. Infect Control Hosp Epidemiol . 2013; 34:875-92.

200. Panel on Antiretroviral Guidelines for Adults and Adolescents, US Department of Health and Human Services (HHS). Guidelines for the use of antiretroviral agents in HIV-1-infected adults and adolescents (February 27, 2024). Updates may be available at HIV.gov website. [Web]

201. Panel on Antiretroviral Therapy and Medical Management of Children Living with HIV, US Department of Health and Human Services (HHS). Guidelines for the use of antiretroviral agents in pediatric HIV infection (June 27, 2024). Updates may be available at HIV.gov website. [Web]

202. Panel on Treatment of HIV-Infected Pregnant Women and Prevention of Perinatal Transmission, US Department of Health and Human Services (HHS). Recommendations for use of antiretroviral drugs in pregnant HIV-1-infected women for maternal health and interventions to reduce perinatal HIV transmission in the United States (January 31, 2024). Updates may be available at HIV.gov website. http://clinicalinfo.hiv.gov/en/guidelines/perinatal/

203. Institute for Safe Medication Practices. ISMP list of error-prone abbreviations, symbols, and dose designations. 2024.