Antiviral nucleoside analogue for herpes infections (HSV-1, HSV-2, VZV)
ATC code: J05AB09 (Famciclovir)
Brand names
Famvir
Prodrug: after oral intake, rapidly deacetylated and oxidised to active penciclovir. In herpes-infected cells, penciclovir is phosphorylated by viral thymidine kinase to penciclovir triphosphate, a competitive inhibitor of viral DNA polymerase. It suppresses replication of HSV-1, HSV-2 and VZV. Oral bioavailability about 77%, three to five times higher than aciclovir. Intracellular half-life of the active metabolite is 7-20 hours, allowing 2-3 daily dosing. No activity against respiratory viruses (rhinoviruses, adenoviruses, parainfluenza, influenza, RSV, SARS-CoV-2).
First line
For genital herpes, famciclovir is used for the primary episode (250 mg three times daily for 5 days) and recurrences (1000 mg twice daily for 1 day or 125 mg twice daily for 5 days). With frequent recurrences (≥6 episodes per year) 2023 recommends suppressive therapy: 250 mg twice daily for 6-12 months, with periodic review. Treatment within 24 hours of recurrence shortens the episode by 1-2 days.
First line
Famciclovir is first-line for herpes zoster in adults. AEDV 2021 and recommend starting therapy within 72 hours of rash onset: 500 mg three times daily for 7 days. Early treatment shortens rash duration, reduces postherpetic neuralgia risk and acute pain. Treatment is mandatory in ophthalmic zoster, second trigeminal branch involvement and immunocompromised patients.
Second line
For recurrent herpes labialis, famciclovir is used as a single-day 1500 mg oral regimen. The Spruance 2006 RCT showed the episode shortens by about 1 day on average (NNT about 10), provided the dose is taken in the prodromal phase (tingling, burning before vesicles appear). If lesions are already established, efficacy is much lower. AEDV positions famciclovir as an alternative to valaciclovir; first line for moderate episodes is topical 1% penciclovir cream.
Adjunct
Early famciclovir in the first 72 hours of herpes zoster reduces the frequency and duration of postherpetic neuralgia. Fewer patients report pain at 3 and 6 months compared with placebo. Once postherpetic neuralgia is established (pain beyond 3 months after rash), famciclovir does not treat it – neuropathic pain drugs are needed (gabapentin, pregabalin, amitriptyline) or 8% capsaicin and 5% lidocaine patches.
The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.
Not recommended
Famciclovir is a nucleoside analogue active against herpesviruses (HSV-1, HSV-2, VZV). It has no activity against rhinoviruses, adenoviruses, parainfluenza, RSV, influenza viruses or SARS-CoV-2 – these viruses lack the thymidine kinase needed to activate famciclovir. The marketing position of famciclovir as a «broad-spectrum antiviral» or «immunomodulator for colds» in the labelling of some Russian generics and in pharmacy advertising is misleading. , AEDV, AEMPS and approved the drug only for the treatment of herpes infections. If famciclovir was prescribed for cold, flu or to «boost immunity», consider seeking a second opinion.
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FDA Category B. Pregnancy experience is limited. AEMPS and AEDV permit use for severe or disseminated zoster and for herpes infections threatening the fetus; in most routine cases aciclovir is preferred because more data are available.
Hale L3. Active penciclovir transfers into milk at concentrations similar to maternal plasma, but no clinical adverse effects in infants have been described. Short courses for zoster or genital herpes are compatible; valaciclovir or aciclovir are preferred for suppressive therapy because more data are available.
Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.
Famciclovir is evaluated for the following indications with varying evidence strength: Herpes zoster (evidence tier A), Genital herpes (evidence tier A), Herpes labialis (evidence tier B). See the full indication matrix with dosing and citations above on this page.
Common side effects of Famciclovir (≥ 1 in 100): Headache, Nausea, Diarrhoea, Rash and itching, Fatigue. See the Safety section for uncommon and serious reactions.
FDA category B. FDA Category B. Pregnancy experience is limited. AEMPS and AEDV permit use for severe or disseminated zoster and for herpes infections threatening the fetus; in most routine cases aciclovir is preferred because more data are available.
Hale L3. Active penciclovir transfers into milk at concentrations similar to maternal plasma, but no clinical adverse effects in infants have been described. Short courses for zoster or genital herpes are compatible; valaciclovir or aciclovir are preferred for suppressive therapy because more data are available.
Famciclovir is contraindicated in: Hypersensitivity to famciclovir, penciclovir or excipients; Severe renal impairment without dose adjustment. Full list in the Safety section.