Famciclovir

Famciclovir, a synthetic acyclic guanine derivative, is a prodrug which after oral administration undergoes rapid first pass metabolism to produce the anti-herpes virus compound, Penciclovir which has an inhibitory activity against herpes simplex virus type 1 (HSV-1) and 2 (HSV-2), and varicella zoster virus (VZV). In cells infected with HSV-1, HSV-2, or VZV, viral thymidine kinase phosphorylates penciclovir to a monophosphate form which is then converted to penciclovir triphosphate by cellular kinase.Penciclovir triphosphate inhibits viral replication by inhibiting viral HSV-2 DNA polymerase competively with deoxyguanosine triphosphate, consequently herpes viral DNA synthesis and, therefore replication is selectively inhibited. Penciclovir triphosphate has an intracellular half-life of 10 hours in HSV-1, 20 hours in HSV-2 and 7 hours in VZV-infected cells. Being converted to penciclovir, no famciclovir is detected in plasma & urine. The absolute bioavailability of penciclovir was found to be 77% when oral dose of 500mg was given and 400mg penciclovir intravenous dose to 12 healthy male patients.

Indications

Treatment of acute herpes zoster, treatment/f suppression of recurrent genital herpes in immunocompetent patients, treatment of recurrent mucocutaneous herpes simplex infections in HIV-infected patients.

Dosage

In herpes zoster 500 mg every 8 hours for 7 days. In immunocompromised patients 500mg tid for 10 days. In first episode of genital herpes 250 mg tid for 5 days.In recurrent genital herpes 125 mg twice daily for 5 days and in immunocompromised patients 500 mg tid for 7 days. In suppression of recurrent genital herpes 250 mg twice daily for up to 1 year. in recurrent orolabial or genital herpes simplex infections, the dose is 500mg twice daily for 7 days. Reduction of dosage is recommended in redu

Contra-Indications

Hypersensitivity.

Special Precautions

No data on the safety of the drug in infants. The pharmacokinetics of famciclovir or penciclovir has not been evaluated in patients below 18years. Dosage adjustment is in needed in renal impairment.

Side Effects

No life threating reactions. Headache, paresthesia, migraine, nausea, diarrhea, vomiting, flatulence, abdominal pain, fatigue, pruritus, rash, and dysmenorrhoea.

Drug Interactions

Clinically significant adverse drug interactions have not been reported. Simultaneous administration with other antiviral compounds such as acyclovir, ganciclovir, or foscarnet gives synergistic effects.