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Therapeutic Classification: antivirals

• Treatment of herpes zoster (shingles).
• Treatment/suppression of genital herpes.
• Reduction of transmission of genital herpes.
• Treatment of chickenpox.
• Treatment of herpes labialis (cold sores).

• Rapidly converted to acyclovir. Acyclovir interferes with viral DNA synthesis.

• Inhibited viral replication, decreased viral shedding, reduced time to healing of lesions.
• Reduced transmission of genital herpes.

Absorption: 54% bioavailable as acyclovir after oral administration of valacyclovir.

Distribution: CSF concentrations of acyclovir are 50% of plasma concentrations.

Metabolism/Excretion: Rapidly converted to acyclovir via intestinal/hepatic metabolism. Primarily excreted in the urine as acyclovir.

Half-life: 2.5–3.3 hr; up to 14 hr in renal impairment (acyclovir).

(plasma concentrations†)

†Acyclovir.

Contraindicated in:

• Hypersensitivity to valacyclovir or acyclovir.

Use Cautiously in:

• Renal impairment (↓ dose/↑ dosing interval recommended if CCr <50 mL/min)
• Pedi: Safety and effectiveness not established in children <18 yr (herpes zoster or genital herpes), <12 yr (herpes labialis), or <2 yr (chickenpox)
• Geri: Dose ↓ may be necessary in older adults due to ↑ risk of acute renal failure and CNS side effects.

GI: nausea, abdominal pain, anorexia, constipation, diarrhea.

GU: crystalluria, RENAL FAILURE.

Hemat: THROMBOTIC THROMBOCYTOPENIC PURPURA/HEMOLYTIC UREMIC SYNDROME (VERY HIGH DOSES IN IMMUNOSUPPRESSED PATIENTS).

Neuro: headache, agitation, confusion, delirium, dizziness, encephalopathy, hallucinations, SEIZURES, weakness.

Drug-Drug:

• Probenecid and cimetidine may ↑ levels and the risk of toxicity, especially in patients with renal impairment.
• Concurrent use of other nephrotoxic drugs↑ risk of adverse renal effects.

Herpes Zoster

• PO (Adults): 1 g 3 times daily for 7 days.

Genital Herpes

• PO (Adults): Initial treatment: 1 g twice daily for 10 days. Recurrence: 500 mg twice daily for 3 days. Suppression of recurrence: 1 g once daily or 500 mg once daily in patients experiencing <10 recurrences/yr. Suppression of recurrence in HIV-infected patients: 500 mg every 12 hr. Reduction of transmission: 500 mg once daily for source partner.

Herpes Labialis

• PO (Adults and Children 12 yr): 2 g initially, then 2 g 12 hr later.

Chickenpox

• PO (Children 2 yr): 20 mg/kg 3 times daily for 5 days (not to exceed 1 g 3 times daily).

(Generic available)

• Tablets: 500 mg; 1 g;

• Assess lesions before and daily during therapy.
• Monitor patient for signs of thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (thrombocytopenia, microangiopathic hemolytic anemia, neurologic findings, renal dysfunction, fever). Requires prompt treatment; may be fatal.

• High Alert:Do not confuse valacyclovir with valganciclovir. Do not confuse Valtrex with Valcyte.
• PO: May be administered without regard to meals.
• Herpes Zoster: Implement valacyclovir therapy as soon as possible after the onset of signs or symptoms of herpes zoster; most effective if started within 48 hr of the onset of zoster rash. Efficacy of treatment started >72 hr after rash onset is unknown.
• Genital Herpes and Herpes Labialis: Implement treatment for genital herpes as soon as possible after onset of symptoms (tingling, itching, burning).
• Chicken Pox: Initiate therapy at the earliest sign or symptom; preferably within 24 hr of onset of rash.

• Instruct patient to take valacyclovir exactly as directed for the full course of therapy. Take missed doses as soon as remembered if not just before next dose; do not double doses. Advise patient to read the Patient Information before starting therapy.
• Advise patient to maintain adequate hydration during therapy.
• Advise patient to notify health care professional promptly if nervous system symptoms (aggressive behavior, unsteady movement, shaky movements, confusion, speech problems, hallucinations, seizures, coma) occur.
• Instruct patient to notify health care professional of all Rx or OTC medications, vitamins, or herbal products being taken and consult health care professional before taking any new medications.
• Instruct females of reproductive potential to notify health care professional if pregnancy is planned or suspected, or if breastfeeding.
• Herpes Zoster: Inform patient that valacyclovir does not prevent the spread of infection to others. Precautions should be taken around others who have not had chickenpox or varicella vaccine, or are immunosuppressed, until all lesions have crusted.
• Genital Herpes and Herpes Labialis: Inform patient that valacyclovir does not prevent the spread of herpes labialis to others. Advise patient to avoid contact with others while lesions or symptoms are present. Valacyclovir reduces transmission of genital herpes to others. Advise patient to practice safe sex (avoid sexual intercourse when lesions are present and wear a condom made of latex or polyurethane during sexual contact).

• Decrease in time to full crusting, loss of vesicles, loss of ulcers, and development of crusts in patients with acute herpes zoster (shingles).
• Decrease in time to full crusting, loss of vesicles, loss of ulcers, and development of crusts in patients with genital herpes.
• Decrease in frequency of outbreaks in patients with genital herpes.
• Decrease in time to full crusting, loss of vesicles, loss of ulcers, and development of crusts in patients with herpes labialis. Decrease in transmission of genital herpes.
• Treatment of chickenpox.

Valtrex