Famciclovir
Famciclovir is an oral antiviral medication used to treat infections caused by herpes viruses, including herpes zoster (shingles), recurrent herpes labialis (cold sores), and recurrent genital herpes. It is converted in the body to its active form penciclovir, which inhibits viral replication by interfering with viral DNA synthesis.
Famciclovir is an antiviral medication that treats herpes virus infections by stopping the virus from multiplying.
Key facts at a glance
- ATC
- J05AB09
- RxNorm
- 68099
- Generic
- Famciclovir
- Class
- atc-j05
- Brands
- —
- Availability
- rx
- Lactation
- unknown
- Routes
- oral
- Forms
- tablet
- Regions
- US, EU, CN, JP
- Monitoring
- —
This page is for informational purposes only.
Do not use this information to diagnose yourself or to replace a physician's advice. Always consult a qualified healthcare provider before starting, stopping, or changing any medication. If you believe you are experiencing a medical emergency, call your local emergency number immediately.
Famciclovir is used to treat herpes zoster (shingles) in immunocompetent adults, recurrent episodes of herpes labialis (cold sores) in immunocompetent adults and adolescents, and recurrent genital herpes in immunocompetent adults. It may also be used for suppression of recurrent genital herpes and treatment of herpes simplex infections in immunocompromised patients.
Famciclovir is a prodrug that is rapidly converted to penciclovir after oral administration. Penciclovir is then phosphorylated by viral thymidine kinase in herpes-infected cells and inhibits viral DNA polymerase, which terminates viral DNA chain elongation and prevents further viral replication.
Famciclovir is most effective when started within 72 hours of shingles onset or at the first sign of a cold sore recurrence. It does not cure herpes infections and does not prevent transmission to others. Common side effects may include headache, nausea, and dizziness. Dosage adjustments may be needed in patients with renal impairment.
Official drug label
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This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed July 26, 2026. · Read our editorial policy