Famciclovir

Famciclovir

  • Pregnancy Category B

Formulations

  • Oral

Dosing

  • Herpes simplex virus (HSV) infections:

    • 1st episode 250 mg 3x/day for 10 days (genital)
    • Recurrent 1 g twice daily for 1 day or 500 mg × 1 dose then 250 mg twice daily for 2 days (genital); 1.5 g × 1 dose (orolabial)
    • Suppression 250 mg twice daily (up to 500 mg twice daily if HIV positive patient)
    • Immunocompromised 500 mg twice daily until lesion resolution

Varicella Zoster infections:

  • Herpes zoster “shingles” 500 mg 3x/day for 7 days to start within 72 hours of symptom onset

  • Prodrug of penciclovir (same mechanism of action of penciclovir): Acyclic nucleoside (similar to acyclovir, viral thymidine kinase dependent, must be tri- phosphorylated to be pharmacologically active). Phosphorylated by herpes thymidine kinase then bi- and tri- phosphorylated by host enzymes leading to viral DNA polymerase inhibition. Incorporates tri-phosphorylated Famciclovir prematurely stopping DNA replication 
  • Bioavailability 77%

FDA

  • Herpes simplex virus (HSV) infections: primary, recurrent, suppressive therapy
  • Varicella and herpes zoster
  • Includes immunocompromised patients

Off-label

  • Recurrent erythema multiforme and other HSV infections (e.g., neonatal HSV, eczema herpeticum)

  • Headache, nausea, diarrhea
  • Thrombocytopenia

  • Probenecid

Considerations for suppressive therapy with antivirals 

  1. 6 or more episodes per year
  2. Lack of prodromal symptoms 
  3. Severe outbreaks
  4. Seronegative partner
  5. Recurrent erythema multiforme

Pregnant women before 36 weeks of gestation to reduce risk of perinatal transmission (who have genital HSV lesion anytime during pregnancy – whether with a primary, non-primary first-episode, or recurrent infection)