Famvir250 mg

Famvir is an antiviral medicine indicated for the treatment and management of specific herpesvirus infections. Indications are classified below by strength of evidence.

FDA-Approved / Established Indications

• Herpes zoster (shingles): Treatment of acute herpes zoster in immunocompetent adults.
• Genital herpes: Treatment of initial and recurrent episodes of genital herpes in immunocompetent adults.
• Suppressive therapy: Chronic suppression of recurrent episodes of genital herpes in immunocompetent adults.
• Recurrent orolabial or genital herpes in HIV-infected patients: Treatment of recurrent mucocutaneous herpes simplex infections in HIV-positive adults.
• Herpes labialis (cold sores): Treatment of recurrent episodes in immunocompetent adults.

Off-Label / Adjunct Use

Famvir is sometimes used off-label for varicella (chickenpox) in select adult patients and for herpes simplex prophylaxis in certain immunocompromised settings, based on clinician judgment; this is not an FDA-approved use and should only be undertaken under specialist supervision.

Each tablet contains Famciclovir INN as the active ingredient. Famciclovir is commonly available in strengths of 125 mg, 250 mg, and 500 mg; exact strengths and available brands may vary by market.

Famvir is a synthetic acyclic guanine derivative and an oral prodrug of penciclovir. After oral administration, Famvir is rapidly and extensively converted to the active antiviral compound, penciclovir, which has demonstrated in-vitro and in-vivo activity against herpes simplex virus types 1 and 2 (HSV-1, HSV-2) and varicella-zoster virus (VZV).

Antiviral agent (nucleoside analogue) — Famvir belongs to the guanine-derivative class of oral antivirals used against herpesviruses.

Mechanism

Famciclovir is a prodrug that is rapidly converted after absorption to penciclovir. Inside virus-infected cells, penciclovir is phosphorylated first by viral thymidine kinase and then by cellular kinases to penciclovir triphosphate, which competitively inhibits viral DNA polymerase and terminates viral DNA chain elongation, thereby suppressing viral replication.

Pharmacokinetics

Following oral administration, Famciclovir is well absorbed and rapidly converted to penciclovir, with an oral bioavailability of penciclovir of approximately 77%. Peak plasma concentrations occur within about 1 hour. Penciclovir is minimally protein bound (less than 20%) and is primarily eliminated unchanged by the kidneys through both glomerular filtration and active tubular secretion, with a plasma elimination half-life of approximately 2 to 3 hours in patients with normal renal function.

Famvir tablets are for oral use. Swallow the tablet whole with a full glass of water; it may be taken with or without food. Begin treatment as soon as possible after symptoms (tingling, pain, or lesion appearance) start, as delayed initiation reduces effectiveness. Complete the entire prescribed course even if symptoms improve early, and take doses at evenly spaced intervals as advised by the physician.

Probenecid: Co-administration with probenecid may increase plasma concentrations of penciclovir (the active metabolite of Famvir) by competing for renal tubular secretion, which can increase the risk of penciclovir-related adverse effects. Monitor patients for toxicity if these drugs must be used together.

Other renally eliminated drugs: Other medicines that reduce renal function or compete for active tubular secretion may theoretically increase penciclovir exposure; caution is advised. No clinically significant interactions have been established with digoxin, or with zidovudine or other antiretrovirals affecting CYP450 metabolism, since Famvir is not significantly metabolized by cytochrome P450 enzymes.

Common (may affect more than 1 in 10 people, indication-dependent)

• Headache
• Nausea

Less Common

• Diarrhea
• Vomiting
• Fatigue
• Paresthesia (tingling/numbness)
• Dizziness

Rare but Serious

• Hypersensitivity reactions, including rash, urticaria, and rarely angioedema or anaphylaxis (see Contraindications and Precautions)
• Confusion or hallucinations, reported mainly in elderly patients or those with renal impairment receiving inappropriately high doses

Patients should seek prompt medical attention if signs of a severe allergic reaction or unusual neurological symptoms occur while taking Famvir.

Pregnancy: Famvir should be used during pregnancy only if clearly needed and if the potential benefit justifies the potential risk to the fetus. Available pharmacovigilance data have not identified a clear drug-associated risk of major birth defects, but controlled human studies are limited. Consult a physician before use in pregnancy.

Lactation: It is not well established whether Famvir/penciclovir passes into human breast milk in clinically significant amounts. Because of the potential for adverse effects in a nursing infant, Famvir should be used during breastfeeding only under medical advice, weighing the benefit of treatment against potential infant exposure.

• Renal impairment: Dose and dosing interval of Famvir must be adjusted according to creatinine clearance; inappropriately high doses in renally impaired patients have been associated with acute renal failure and CNS adverse effects.
• Elderly patients: Use with caution due to age-related decline in renal function; dose adjustment may be necessary and patients should be monitored for CNS effects such as confusion.
• Immunocompromised patients: Use for herpes infections in HIV-infected or other immunocompromised patients should be under close medical supervision.
• Hypersensitivity: Discontinue Famvir immediately and seek medical attention if signs of a hypersensitivity reaction occur (see Contraindications).
• Take Famvir exactly as prescribed by your physician; do not stop, extend, skip doses, or share this medicine with others without medical advice, to ensure effective viral suppression and reduce the chance of prolonged illness.

Limited data are available on Famvir overdose. Reported effects following excessive dosing (particularly in patients with renal impairment) include acute renal failure and central nervous system symptoms such as confusion. In case of suspected overdose, seek immediate medical attention or contact a poison control center/emergency services right away; do not attempt home treatment. Supportive care is the mainstay of management, and hemodialysis may help remove penciclovir from the circulation in significant overdose, particularly in patients with renal impairment.

Store at room temperature (below 30°C), away from light and moisture. Keep out of reach of children.

Renal Impairment

Dose and/or dosing frequency of Famvir must be reduced based on creatinine clearance; consult indication-specific renal dosing tables in the full prescribing information. Use with caution and close monitoring.

Hepatic Impairment

No dose adjustment is generally required in mild-to-moderate hepatic impairment; data in severe hepatic impairment are limited, so use with caution.

Elderly

Age-related decline in renal function should be considered; dose adjustment per renal function is recommended, with monitoring for CNS side effects.

Pediatric Patients

Safety and efficacy of Famvir have not been established in pediatric patients; see Pediatric Uses.

HIV-Infected Patients

Famvir is used under medical supervision for recurrent orolabial or genital herpes in this population at the recommended dose and duration.

Duration of Famvir therapy depends on the indication: a single dose for herpes labialis, 1 day for recurrent genital herpes, 7 days for herpes zoster and for recurrent herpes in HIV-infected patients, 7–10 days for initial genital herpes, and up to 1 year (with periodic physician reassessment) for suppressive therapy of recurrent genital herpes. The complete prescribed duration should always be finished as directed by the physician.

Antiviral agents; Nucleoside analogues; Synthetic acyclic guanine derivatives

Famciclovir itself is inactive and is rapidly converted after absorption to penciclovir. In cells infected with herpes simplex virus or varicella-zoster virus, viral thymidine kinase phosphorylates penciclovir to its monophosphate form, which is then further phosphorylated by cellular kinases to penciclovir triphosphate. This active triphosphate competitively inhibits viral DNA polymerase, becoming incorporated into and terminating the growing viral DNA chain, thereby halting viral DNA replication without significantly affecting normal host cell DNA synthesis.

B (legacy FDA pregnancy classification used prior to the 2015 Pregnancy and Lactation Labeling Rule; current labeling uses narrative risk description instead of a letter category)

The safety and efficacy of Famvir have not been established in pediatric patients. Famvir is therefore not generally recommended for use in children unless specifically directed and closely supervised by a pediatric specialist, who will weigh potential benefits against the lack of established pediatric dosing and safety data.