Famciclovir (Famvir®)


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.


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


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.


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.


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