Reviewed on 1/19/2022

What Is Famciclovir and How Does It Work?

Famciclovir is a prescription medication used to treat Acute Herpes Zoster (Shingles), Herpes Labialis, Genital Herpes, and Herpes (HIV-Infected Adults). 

  • Famciclovir is available under the following different brand names: Famvir

Dosages of Famciclovir

Adult dosage


  • 125mg
  • 250mg
  • 500mg

Acute Herpes Zoster (Shingles)

Adult dosage

Treatment in immunocompetent adults

  • 500 mg orally every 8 hours for 7 days; initiated within 72 hours of symptom or lesion onset

Herpes Labialis

Adult dosage

  • Initial episode: 250 mg orally every 8 hours for 7-10 days
  • Suppressive therapy: 250 mg orally every 12 hours for 12 months
  • Recurrent episodes: 1500 mg orally once; initiate therapy at first sign (within 1 hour) of symptoms such as tingling, itching or burning

Genital Herpes

Adult dosage

  • Suppressive therapy: 250 mg orally every 12 hours for up to 12 months
  • Recurrent episodes: 1000 mg orally every 12 hours for 1 day; initiated within 6 hours of symptom or lesion onset

Herpes (HIV-Infected Adults)

Adult dosage

  • Prevention of HSV reactivation: 500 mg orally every 12 hours
  • Recurrent episodes: 500 mg orally every 12 hours for 5-10 days; initiated within 48 hours of symptom or lesion onset

Dosage Considerations – Should be Given as Follows: 

  • See "Dosages."

What Are Side Effects Associated with Using Famciclovir?

Common side effects of Famciclovir include:

  • headache, and 
  • nausea

Serious side effects of Famciclovir include:

  • hives, 
  • difficult breathing, 
  • swelling in the face or throat, 
  • confusion, 
  • little or no urination, 
  • swelling in the feet or ankles, 
  • tiredness, and
  • shortness of breath

Rare side effects of Famciclovir include:

  • none 

This is not a complete list of side effects and other serious side effects or health problems may occur as a result of the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may report side effects or health problems to FDA at 1-800-FDA-1088.


A Timeline of the HIV/AIDS Pandemic See Slideshow

What Other Drugs Interact with Famciclovir?

If your medical doctor is using this medicine to treat your pain, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider or pharmacist first.

  • Famciclovir has severe interactions with the following drugs:
    • varicella virus vaccine live
    • zoster vaccine live
  • Famciclovir has serious interactions with the following drug:
    • talimogene laherparepvec 
  • Famciclovir has moderate interactions with the following drugs:
  • Famciclovir has minor interactions with the following drugs:

This information does not contain all possible interactions or adverse effects. Visit the RxList Drug Interaction Checker for any drug interactions. Therefore, before using this drug, tell your doctor or pharmacist of all the drugs you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist. Check with your physician if you have health questions or concerns.

What Are Warnings and Precautions for Famciclovir?


  • Known hypersensitivity to this drug or its active metabolite, penciclovir.

Effects of drug abuse

  • None

Short-Term Effects

  • See “What Are Side Effects Associated with Using Famciclovir?”

Long-Term Effects

  • See “What Are Side Effects Associated with Using Famciclovir?”


  • Dosage must be adjusted in renal impairment; there is a risk of acute renal failure (ARF) with inappropriately high dosage. 
  • Patients with galactose intolerance, glucose-galactose malabsorption syndrome, or severe lactase deficiency should discuss it with practitioner (famciclovir tablets contain lactose)

Pregnancy and Lactation

  • Healthcare providers are encouraged to report pregnancies and pregnancy outcomes to Novartis Adverse Event reporting line at 1-888-NOW-NOVA (669-6682)
  • Available data from pharmacovigilance reports in pregnant women have not identified a drug- associated risk of major birth defects, miscarriage or adverse maternal or fetal outcomes; there are risks to fetus associated with untreated herpes simplex virus during pregnancy; after oral administration, famciclovir (prodrug) is converted to penciclovir (active drug); in animal reproduction studies with famciclovir, no evidence of adverse developmental outcomes observed at systemic exposures of penciclovir (AUC) slightly higher than those at maximum recommended human dose (MRHD)
  • The risk of neonatal herpes infection varies from 30% to 50% for genital herpes simplex virus (HSV) infections that occur in late pregnancy (third trimester), whereas in early pregnancy, infection carries a risk of about 1%; primary herpes outbreak during first trimester of pregnancy associated with neonatal chorioretinitis, microcephaly and, in rare cases, skin lesions; in very rare cases, transplacental transmission can occur resulting in congenital infection, including microcephaly, hepatosplenomegaly, intrauterine growth restriction and stillbirth; co-infection with HSV increases the risk of perinatal HIV transmission in women who had a clinical diagnosis of genital herpes during pregnancy
  • Effects on reproductive potential
    • Decreased fertility, due to testicular toxicity, observed in male animals following repeated administration of famciclovir or penciclovir; no evidence of significant effects on sperm count, motility or morphology during treatment or during an 8-week follow-up 
    • There are no data on presence of famciclovir (prodrug) or penciclovir (active drug) in human milk, effects on breastfed infant, or on milk production; animal data indicate that penciclovir is present in the milk of lactating rats; developmental and health benefits of breastfeeding should be considered along with mother’s clinical need for therapy and any potential adverse effects on breastfed infant from therapy or from underlying maternal condition.
Medscape. Famciclovir.


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