Pharm

Foscarnet

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Foscarnet, Foscavir, Phosphonoformic Acid

  • See Also
  1. Cytomegalovirus Retinitis
  2. Cidofovir
  3. Ganciclovir
  4. Valganciclovir
  5. Letermovir
  6. Maribavir
  • Indications
  1. Cytomegalovirus Retinitis (HIV Infection)
  2. HSV Infection (Acyclovir-resistant) in Immunocompromised patients
    1. Also used for Acyclovir-resistant VZV (off-label)
  • Contraindications
  1. Children (relative contraindication)
    1. May be used if benefit outweighs risk
  • Mechanism
  1. Synthetic analog of inorganic pyrophosphate
  2. Selectively blocks viral DNA Polymerases at their pyrophosphate binding site, preventing DNA Replication
  3. Crosses the blood brain barrier
  • Dosing
  1. Prehydrate before Foscarnet infusion
    1. Normal Saline 750 to 1000 ml for doses 90 to 120 mg/kg
    2. Normal Saline 500 ml for doses 40 to 60 mg/kg
  2. Cytomegalovirus Retinitis
    1. First 2 to 3 weeks
      1. Give 60 mg/kg IV over 1 hour every 8 hours OR
      2. Give 90 mg/kg IV over 1.5 to 2 hours every 12 hours
    2. Next
      1. Give 90 to 120 mg/kg IV over 2 hours daily
  3. HSV Infection (Acyclovir-resistant)
    1. 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
  • Adverse Effects
  1. Less well tolerated than Ganciclovir
  2. Nephrotoxicity
    1. Typically resolves on stopping medication, but Hemodialysis has been needed for some patients
  3. Anemia
  4. Granulocytopenia
  5. Phlebitis
  6. Nausea or Vomiting
  7. Genital Ulcers
    1. Ulcers secondary to local urine irritation
  8. Tooth deposits
    1. Seen in young animals
  9. Electrolyte abnormalities
    1. Foscarnet contains high Sodium concentration (10 meq or 460 mg per mg Foscarnet)
    2. Hypocalcemia, Hypomagnesemia and Hypokalemia
    3. Avoid rapid infusion (risk of secondary QTc Prolongation, Seizures)
  • Safety
  1. Unknown safety in pregnancy
  2. Unknown safety in Lactation
  • Drug Interactions
  1. Nephrotoxic Drugs
  2. Pentamidine
    1. Hypocalcemia risk
  • Resources
  1. Foscarnet Injection Solution (DailyMed)
    1. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=90e3da4e-3b1f-428b-99ca-e4bed1c80028
  • References
  1. (2013) Med Lett Drugs Ther 11(127): 19-30 [PubMed]
  2. (1992) Med Lett Drugs Ther 34(861): 3-4 [PubMed]