foscarnet

Absorption: IV administration results in complete bioavailability.

Distribution: Variable penetration into CSF. May concentrate in and be slowly released from bone.

Metabolism/Excretion: 80–90% excreted unchanged in urine.

Half-Life: 3 hr (in patients with normal renal function); longer half-life of 90 hr may reflect release of drug from bone.

Time/Action Profile ⬆ ⬇

ROUTE	ONSET	PEAK	DURATION
IV	rapid	end of infusion	8–24 hr

Contraind./Precautions ⬆ ⬇

Contraindicated in:

Hypersensitivity;
HF (due to sodium content);
Patients on sodium-restricted diets;
Hemodialysis;
Lactation: Lactation.

Use Cautiously in:

Renal impairment (dose ↓ required if CCr ≤1.4–1.6 mL/min/kg);
Seizure disorders;
QT interval prolongation or cardiovascular disease;
Hypokalemia or hypomagnesemia (must be corrected prior to therapy);
OB: Safety not established in pregnancy;
Pedi: Safety and effectiveness not established in children.

Adv. Reactions/Side Effects ⬆ ⬇

CV: chest pain, edema, palpitations, QT interval prolongation, TORSADES DE POINTES

Derm: ↑sweating, pruritus, rash, skin ulceration

EENT: conjunctivitis, eye pain, vision abnormalities

F and E: hypocalcemia, hypokalemia, hypomagnesemia, hyperphosphatemia, hypophosphatemia

GI: diarrhea, nausea, vomiting, abdominal pain, abnormal taste sensation, anorexia, constipation, dyspepsia

GU: renal failure, albuminuria, dysuria, nocturia, polyuria, urinary retention

Hemat: anemia, leukopenia, neutropenia

Local: pain/inflammation at injection site

MS: arthralgia, myalgia, back pain, involuntary muscle contraction

Neuro: headache, anxiety, ataxia, confusion, depression, dizziness, fatigue, hypoesthesia, neuropathy, paresthesia, SEIZURES, tremor, weakness

Resp: cough, dyspnea

Misc: fever, chills, flu-like syndrome, HYPERSENSITIVITY REACTIONS (INCLUDING ANAPHYLAXIS, URTICARIA, AND ANGIOEDEMA), MALIGNANCY

Interactions ⬆ ⬇

Drug-drug:

QT interval prolonging medications, including quinidine, procainamide, amiodarone, sotalol, chlorpromazine, thioridazine, moxifloxacin, pentamidine, and methadone, may ↑ risk of QT interval prolongation; avoid concurrent use.
Concurrent use with parenteral pentamidine may result in severe, life-threatening hypocalcemia.
Risk of nephrotoxicity may be ↑ by concurrent use of other nephrotoxic agents, including amphotericin B, aminoglycosides, cyclosporine, acyclovir, methotrexate, tacrolimus, and pentamidine (IV).

Route/Dosage ⬆ ⬇

Cytomegalovirus Retinitis

IV (Adults ): 60 mg/kg every 8 hr or 90 mg/kg every 12 hr for 2–3 wk, then 90–120 mg/kg/day as a single dose. Dose ↓ required for any degree of renal impairment.

Herpes Simplex Virus

IV (Adults ): 40 mg/kg every 8–12 hr for 2–3 wk or until healing occurs.

Availability ⬆ ⬇

(Generic available)

Solution for injection: 24 mg/mL

Assessment ⬆ ⬇

Monitor ECG periodically during therapy for QT interval prolongation.
CMV Retinitis: Diagnosis of CMV retinitis should be determined by ophthalmoscopy before treatment with foscarnet. Ophthalmologic examinations should also be performed at the conclusion of induction and every 4 wk during maintenance therapy.
Culture for CMV (urine, blood, throat) may be taken before administration. However, a negative CMV culture does not rule out CMV retinitis.
HSV Infections: Assess lesions before and daily during therapy.

Lab Test Considerations:

Monitor serum creatinine before and 2–3 times weekly during induction therapy and at least once every 1–2 wk during maintenance therapy. Monitor 24-hr CCr before and periodically throughout therapy. If CCr drops below 0.4 mL/min/kg, discontinue foscarnet.
- Monitor serum calcium, magnesium, potassium, and phosphorus before and 2–3 times weekly during induction therapy and at least weekly during maintenance therapy. May cause ↓ concentrations.
- May cause anemia, granulocytopenia, leukopenia, and thrombocytopenia. May cause ↑ AST and ALT levels and abnormal A-G ratios.

Implementation ⬆ ⬇

Adequately hydrate patient with 750–1000 mL of 0.9% NaCl or D5W before first infusion to establish diuresis, then administer 750–1000 mL with 120 mg/kg of foscarnet or 500 mL with 40–60 mg/kg of foscarnet with each dose to prevent renal toxicity.

IV Administration:

Intermittent Infusion: Diluent: May be administered via central line undiluted. If administered via peripheral line, must be diluted with D5W or 0.9% NaCl to prevent vein irritation. Do not administer solution that is discolored or contains particulate matter. Do not refrigerate or freeze; stable for 24 hr at room temperature. Use diluted solution within 24 hr.Concentration: Undiluted: 24 mg/mL; Diluted: 12 mg/mL.
- Dose is based on patient weight; excess solution may be discarded from bottle before administration to prevent overdosage.
- Patients who experience progression of CMV retinitis during maintenance therapy may be retreated with induction therapy followed by maintenance therapy.
Rate: Administer at a rate not to exceed 1 mg/kg/min.
- Infuse solution via infusion pump to ensure accurate infusion rate.

Patient/Family Teaching ⬆ ⬇

Inform patient that foscarnet is not a cure for CMV retinitis. Progression of retinitis may continue in immunocompromised patients during and after therapy. Advise patients to have regular ophthalmologic exams.
May cause dizziness and seizures. Caution patient to avoid driving or other activities requiring alertness until response to medication is known.
Advise patient to notify health care professional immediately if perioral tingling or numbness in the extremities or paresthesia occurs during or after infusion. If these signs of electrolyte imbalance occur during administration, infusion should be stopped and lab samples for serum electrolyte concentrations obtained immediately.
Emphasize the importance of frequent follow-up exams to monitor renal function and electrolytes.

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Pronunciation ⬇

Classifications ⬆ ⬇

Indications ⬆ ⬇

Action ⬆ ⬇

Pharmacokinetics ⬆ ⬇