Famciclovir (Famvir®)

Class:

Famciclovir is a prodrug of penciclovir.

Antiviral Activity:

Famciclovir has activity against herpesviruses and hepatitis B virus.

Mechanism of Action:

Famciclovir is converted to penciclovir, which is converted to the triphosphate form (penciclovir triphosphate). Penciclovir triphosphate selectively inhibits viral DNA polymerase by competing with deoxyguanosine triphosphate.

Mechanism of Resistance:

The primary mechanism of resistance to famciclovir is related to viral thymidine kinase (TK) and DNA polymerase mutations.

Pharmacodynamics:

No relationship has been established between the effective in vitro and in vivo concentrations.

Pharmacokinetics:

Famciclovir is absorbed in the duodenum and is converted to penciclovir by first-pass hepatic (pre-systemic) metabolism. The absolute bioavailability of penciclovir after oral famciclovir is 77%. Renal excretion is the major route of elimination of penciclovir.

Adverse Effects:

Common adverse effects are fatigue, headache, nausea, vomiting and GI upset.

Dosage:

Tablet 125mg, 250mg, 500mg

See table for specific dosing

Disease state based dosing:

Renal Impairment:

See text

Hepatic Impairment:

No dose adjustment is necessary

Drug Interactions:

Probenecid – may impair the clearance of the active metabolite of famciclovir, penciclovir. Therefore concomitant administration should be avoided.

Pregnancy:

Category B: No evidence of risk in humans but studies inadequate.

Monitoring Requirements:

Baseline serum creatinine/BUN

Brand names/Manufacturer:

Famvir®/Novartis Pharmaceuticals Corp Dba Sandoz Pharmaceuticals Corp