Section 15 · Monograph
Foscarnet
Reviewed Nov 2026FDA label
FoscavirAntiviral (pyrophosphate analog)
- Forms
- IV: 24mg/mL (250, 500mL)
- Dose
- CMV CNS disease: 60mg/kg IV every 8h or 90mg/kg every 12h (renal adjustment); pre-hydrate
- MOA
- Directly inhibits viral DNA polymerase
Black Box Warning
- Renal impairment is the major toxicity; adequate hydration and renal monitoring are required
- Seizures related to alterations in plasma minerals and electrolytes have been associated with treatment — monitor electrolytes and correct promptly
Indications
- CMV retinitis in AIDS patientsFDA-labeled
- Acyclovir-resistant HSV mucocutaneous infection in immunocompromised patientsFDA-labeled
Off-Label Uses
- CMV encephalitis and polyradiculitis (often combined with ganciclovir)Off-label
Mechanism of Action
- Pyrophosphate analog that directly inhibits viral DNA polymerase without requiring phosphorylation, active against ganciclovir-resistant CMV
Full Dosing
Adult / usual
- CMV induction: 60mg/kg IV every 8 hours or 90mg/kg every 12 hours for 14-21 days; maintenance 90-120mg/kg once daily
- Infuse by pump over at least 1 hour (2 hours for 90mg/kg doses)
Renal
- Dose adjusted to CrCl; give 750-1,000mL normal saline before the first dose and with each infusion
Contraindications
- Hypersensitivity to foscarnet
Drug Interactions
- Nephrotoxic drugs (aminoglycosides, amphotericin B, IV pentamidine, cyclosporine, tacrolimus): additive toxicity
- QT-prolonging drugs and drugs that lower calcium or magnesium
Adverse Effects
- Nephrotoxicity
- Hypocalcemia, hypomagnesemia, hypo- or hyperphosphatemia, hypokalemia
- Seizures and paresthesias
- Anemia, nausea, genital ulceration
Monitoring Parameters
- Serum creatinine and CrCl before each dose adjustment, 2-3 times weekly
- Calcium (ionized), magnesium, potassium and phosphorus
- ECG when electrolytes are abnormal
Pregnancy & Lactation
- Limited human data; teratogenic risks in animals — use only if benefit justifies risk
- Breastfeeding not recommended