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famciclovir

S01AD07

Forms & Strengths

Oral tablets: 125 mg, 250 mg, 500 mg

Adult Dosing

Herpes zoster: 500 mg orally every 8 hours for 7 days
Genital herpes (initial episode): 250 mg orally every 8 hours for 7 to 10 days
Genital herpes (recurrence): 125 mg orally twice daily for 5 days or 1000 mg twice daily for 1 day
Genital herpes (suppressive therapy): 250 mg orally twice daily
Labial herpes (cold sores): 1500 mg as a single dose
Immunocompromised genital herpes recurrence: 500 mg orally twice daily for 7 days

Pediatric Dosing

Safety and efficacy in pediatric patients (<18 years) have not been established

Indications

Treatment of acute herpes zoster (shingles)
Treatment and suppression of recurrent genital herpes
Treatment of recurrent episodes of herpes labialis (cold sores) in immunocompetent hosts
Treatment of recurrent mucocutaneous herpes simplex infections in HIV-infected patients

Mechanism of Action

Prodrug of penciclovir; rapidly converted to penciclovir in vivo
Penciclovir is phosphorylated by viral thymidine kinase into penciclovir triphosphate
Inhibits viral DNA polymerase and competes with deoxyguanosine triphosphate
Terminates viral DNA chain elongation, halting herpes simplex virus (HSV-1, HSV-2) and varicella-zoster virus (VZV) replication

Contraindications

Hypersensitivity to famciclovir, penciclovir, or any component of the formulation
Severe hypersensitivity reactions (e.g., anaphylaxis, toxic epidermal necrolysis)

Adverse Reactions

Headache
Nausea
Fatigue
Diarrhea
Dizziness
Abdominal pain
Rare: Acute renal failure, severe hypersensitivity (urticaria, angioedema), hallucinations

Drug Interactions

Probenecid: May increase plasma concentrations of penciclovir by decreasing renal excretion
Digoxin: Minor increases in digoxin concentrations possible
No significant cytochrome P450-mediated drug interactions expected

Curated Content: Needs Vetting Before Put to Clinical Use