II. Indications
- Cytomegalovirus Retinitis (HIV Infection)
-
HSV Infection (Acyclovir-resistant) in Immunocompromised patients
- Also used for Acyclovir-resistant VZV (off-label)
III. Contraindications
- Children (relative contraindication)
- May be used if benefit outweighs risk
IV. Mechanism
- Synthetic analog of inorganic pyrophosphate
- Selectively blocks viral DNA Polymerases at their pyrophosphate binding site, preventing DNA Replication
- Crosses the blood brain barrier
V. Dosing
- Prehydrate before Foscarnet infusion
- Normal Saline 750 to 1000 ml for doses 90 to 120 mg/kg
- Normal Saline 500 ml for doses 40 to 60 mg/kg
-
Cytomegalovirus Retinitis
- First 2 to 3 weeks
- Give 60 mg/kg IV over 1 hour every 8 hours OR
- Give 90 mg/kg IV over 1.5 to 2 hours every 12 hours
- Next
- Give 90 to 120 mg/kg IV over 2 hours daily
- First 2 to 3 weeks
-
HSV Infection (Acyclovir-resistant)
- Give 40 mg/kg IV over 1 hour (no faster than 1 mg/kg/min) every 8 to 12 hours for 2 to 3 weeks
VI. Adverse Effects
- Less well tolerated than Ganciclovir
- Nephrotoxicity
- Typically resolves on stopping medication, but Hemodialysis has been needed for some patients
- Anemia
- Granulocytopenia
- Phlebitis
- Nausea or Vomiting
-
Genital Ulcers
- Ulcers secondary to local urine irritation
-
Tooth deposits
- Seen in young animals
-
Electrolyte abnormalities
- Foscarnet contains high Sodium concentration (10 meq or 460 mg per mg Foscarnet)
- Hypocalcemia, Hypomagnesemia and Hypokalemia
- Avoid rapid infusion (risk of secondary QTc Prolongation, Seizures)
VII. Safety
- Unknown safety in pregnancy
- Unknown safety in Lactation
VIII. Drug Interactions
IX. Resources
- Foscarnet Injection Solution (DailyMed)