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 medication 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.


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) (cold sores, genital herpes) and herpes zoster (shingles, chickenpox). It is also 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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Famciclovir is used to treat:

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


How does Famciclovir work?

Famciclovir is a prodrug, which means that once it is swallowed it converts into another drug, penciclovir. Famciclovir is much better absorbed than penciclovir, which ensures that more of the drug reaches its target.


Once inside a cell, penciclovir inhibits replication of viral DNA, thereby stopping the herpes virus from replicating and spreading.


Famciclovir can be taken for the management of herpes long-term. This is referred to as suppressive therapy. Studies have shown that doses of 125 mg to 250 mg 2 to 3 times a day, are 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 within 48 hours after taking the medication.


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 as follows:

  • Dizziness 
  • Headaches
  • Pains
  • Diarrhea
  • Nausea and vomiting
  • Sore throat
  • Skin rash


Research has shown that the severity of these side effects does not increase as the dose is increased. Patients who were given 125 mg of famciclovir per day experienced similar side effects to 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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