What is Famciclovir used for?

What you need to know about the medication used to treat genital herpes, cold sores, shingles, and even herpes in cats.


Famciclovir is an antiviral prescription drug used in the treatment of infections caused by major types of herpes virus. A cure for herpes does not exist but antiviral medications can help patients to manage their symptoms more easily.


What is Famciclovir and what is Famciclovir used for?

Famciclovir (also known as Famvir) is an oral tablet taken to treat infections caused by herpes simplex type 1 (HSV 1) and type 2 (HSV 2) (genital herpes, cold and fever sores) and herpes zoster (shingles, chickenpox). It has also been shown to be effective against the Epstein Barr virus.

Generic Famvir is available under various names. Each oral tablet contains a dose of 500 mg of famciclovir.

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Pregnant women and HIV patients can also be prescribed famciclovir to treat and prevent herpes outbreaks.


Famciclovir is used to treat:

  • Cold sores
  • Genital herpes
  • Shingles
  • Chickenpox
  • Fever blisters
  • Glandular fever


Famciclovir for cats

Although it is predominantly a human drug, famciclovir is used to treat feline herpes virus infections. Speak to a vet if you think your cat may have herpes.


How does Famciclovir work?

Famciclovir 500 mg is a prodrug, which means that once it is swallowed it converts into penciclovir. It is much better absorbed than penciclovir on its own. This ensures that more of the drug reaches the target cells containing the virus.


Once inside the cell, penciclovir inhibits replication of the viral DNA and thereby stops the herpes virus from spreading further.


Famciclovir can be taken for the management of herpes long-term. This is referred to as suppressive therapy. Studies have shown that at doses of 125 mg to 250 mg 2 to 3 times a day, the drug is effective in suppressing genital herpes outbreaks in patients who previously had 6 or more herpes outbreaks a year.


How long does Famciclovir take to work?

Once absorbed, famciclovir will usually begin to work immediately. But it may take a couple of days for patients to notice an effect.


It’s important to take Famvir as soon as signs of an outbreak become apparent, because the longer you wait, the longer it will take to treat a flare-up.


In mild to moderate cases of genital herpes, it can take 48 hours for symptoms to ease.


For shingles, it can take around 72 hours to notice an improvement.


Cold sores and blisters will usually take 2 to 4 weeks to heal completely, but associated symptoms such as fever or pain should go away 48 hours after taking famciclovir.


How long does Famciclovir stay in your system?

With a typical half-life of 10 to 20 hours, you should expect famciclovir to stay in your system for a few days.


Famciclovir side effects (long-term)

The most frequently observed side effects after taking famciclovir are headaches, nausea, and diarrhea. Some studies also report dizziness as a side effect.


The following side effects can be expected when taking Famvir:

  • Dizziness or nausea
  • Headaches
  • Pains
  • Diarrhea
  • Vomiting
  • Sore throat
  • Skin rash


Researchers have also shown that the severity of these side effects does not increase as doses increase. Patients who were given 125 mg of famciclovir per day experienced similar side effects as those given the maximum dose of 2,250 mg a day.


There is scientific evidence that the medication is safe when used long-term. If you are taking Famvir for the purpose of herpes suppression, your doctor may prescribe the medication for up to 1 year and then schedule a follow-up visit.


It may be safe to take the drug during pregnancy, but there aren’t many clinical studies to confirm the effects on the unborn child. Women who are pregnant should consult their doctor. Alternative antivirals such as valacyclovir and acyclovir have been extensively studied and are deemed safe for use during pregnancy.



If you have questions or aren’t entirely sure about what famciclovir is used for, speak to your doctor or healthcare provider.



  1. (2019). Famvir. Retrieved November 3, 2019, from website:
  2. De Paor, M., O'Brien, K., Fahey, T., & Smith, S. M. (2016). Antiviral agents for infectious mononucleosis (glandular fever). The Cochrane database of systematic reviews, 12(12), CD011487.
  3. Diaz-Mitoma, F. (1998). Oral Famciclovir for the Suppression of Recurrent Genital Herpes<SUBTITLE>A Randomized Controlled Trial</SUBTITLE>. JAMA, 280(10), 887.
  4. Novartis. (2016). Famvir. Retrieved from

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