Famciclovir is an oral prodrug antiviral agent of penciclovir, a guanosine analogue. It is indicated for the treatment of acute herpes zoster (shingles) and for the treatment or suppression of recurrent episodes of genital herpes in immunocompetent patients. It is also used for the management of herpes labialis (cold sores). Famciclovir is rapidly converted to penciclovir in the body, which inhibits viral DNA synthesis and replication.
Adult: Herpes Zoster: 500 mg every 8 hours for 7 days. Recurrent Genital Herpes (Treatment): 125 mg twice daily for 5 days. Suppression of Genital Herpes: 250 mg twice daily for up to 1 year. Herpes Labialis: 1500 mg as a single dose.
Note: Can be taken with or without food. Swallow the tablet whole with a glass of water. For herpes zoster, initiate therapy at the earliest sign or symptom (within 72 hours of rash onset is most effective). For recurrent episodes, initiate at the first sign or symptom.
Famciclovir is a prodrug of penciclovir. After oral administration, it is rapidly converted to penciclovir. Penciclovir is phosphorylated by viral thymidine kinase to penciclovir monophosphate, which is then further phosphorylated by cellular kinases to penciclovir triphosphate. This active form competitively inhibits viral DNA polymerase, thereby inhibiting viral DNA synthesis and replication.
Pregnancy: Pregnancy Category B. Animal studies have shown no direct harm, but there are no adequate and well-controlled studies in pregnant women. Use only if the potential benefit justifies the potential risk to the fetus.
Driving: May cause dizziness, somnolence, or confusion. Patients should be cautioned about operating machinery or driving until they know how the drug affects them.
| Probenecid | Increases plasma concentration of penciclovir by reducing its renal tubular secretion. May increase risk of side effects. | Moderate |
| Digoxin | Famciclovir may slightly increase the plasma concentration of digoxin. Monitoring of digoxin levels is advised. | Moderate |
| Theophylline | Potential for increased theophylline levels; clinical significance unknown. Monitor for toxicity. | Low |
| Other drugs eliminated by active renal tubular secretion (e.g., cimetidine) | Potential for increased plasma levels of either drug. | Low |
Same composition (Famciclovir (250mg)), different brands: