Manage genital herpes outbreaks with Famiciclovir (generic Famvir)

This antiviral medication effectively treats the symptoms of both genital herpes and cold sores, especially when you take it early on. It also can prevent new outbreaks.

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Written by Dr Yasmin Aghajan, MD

Information last reviewed 07/15/19


What is Famciclovir and how does it work?

Famciclovir is an antiviral medication that works by inhibiting the DNA of viruses from replicating, so that the virus cannot multiply. It is used to treat the virus that causes cold sores, Herpes Simplex 1, or HSV-1, and the virus that usually causes genital herpes, HSV-2. HSV-1/HSV-2 first enters the body via the skin, mouth, or genitals, and migrates to the nerves. There, it can stay quiet, or “dormant” for a period of time before reactivating and causing symptoms. Symptoms of a genital herpes outbreak  include pain, burning, tingling and itching between 6 hours to 4 days before the actual sore appears. This period is called the “prodrome” and treatment is most effective when started as soon as possible. The available treatments for genital herpes are Acyclovir, Valacyclovir, and Famciclovir. The benefit of Famciclovir is it has a shorter treatment duration. 

How quickly does Famciclovir work?

Famciclovir works best when taken at the earliest sign of an outbreak. Although the medication will take effect immediately, you may not start to have relief until several hours or days after starting treatment. Treatment shortens the  time it takes to heal and decreases the duration of viral shedding (contagious period).


Active ingredients

The active ingredient in Famciclovir is the antiviral drug famciclovir (500mg)

Inactive ingredients

Famciclovir contains the following inactive ingredients: hydroxypropyl cellulose, hydroxypropyl methylcellulose, lactose, magnesium stearate, polyethylene glycols, sodium starch glycolate and titanium dioxide.

The ingredients may vary by manufacturer; the ingredients listed above are the ingredients in Famvir.

Which ingredients can cause an allergic reaction?

Symptoms of a severe allergic reaction to this medication include facial swelling, hives, dizziness, itchy throat or difficulty breathing. While a severe allergic reaction to this medication is rare, if you do notice these symptoms shortly after taking the medication, please seek medical attention right away. 


Famciclovir dosage

For the first episode of genital herpes, the treatment dosage is:

  • Famciclovir 250mg three times a day for 7 to 10 days.

The dosage of Famciclovir to treat a recurrent episode of genital herpes (i.e., you have had genital herpes in the past and this is a recurrence) is:

  • 1000mg twice daily, for a single day
  • OR 125mg twice daily for five days
  • OR 500mg once, followed by 250mg twice daily for two days.

The treatment works best when started at the first symptom and within 72 hours (ie. tingling, itching, burning, pain or an eruption). 

The dosage of Famciclovir to treat cold sores (herpes labialis) is 1,500mg (3 x 500mg tablets) as a single dose. Treatment works best when started at the first symptom (ie. tingling, itching, burning, pain or an eruption around the lips). 

How to take Famciclovir

Take the dosage and treatment length prescribed. Famciclovir does not have to be taken with food. 

Side Effects


  • If taken in excessively high doses in patients with underlying kidney disease, Famciclovir can cause kidney failure.

  • Famciclovir is not a cure for herpes; you could still pass the virus onto others while being treated.

  • Let your doctor know if you have kidney disease, as the dose may have to be reduced based on your kidney function.

  • Let your doctor know if you have HIV or are immunocompromised.

Famciclovir side effects

The most common side effects of Famciclovir are headaches and nausea. A range of other side effects ahve been reported. It is important that you always read the patient information leaflet before taking any medication, including Famiciclovir. 

Drug interactions

There are very few drug interactions with Famciclovir. Some include: Cladribine, Talimogene Laherparepvec, Varicella virus vaccine, and Zoster vaccine (do not take this medication within 2 weeks of these vaccinations because it may make the vaccines less effective). 


Famciclovir is contraindicated if you have an allergy to it or any of its ingredients. 
Famvir contains lactose; if you have a rare genetic problem of galactose intolerance or lactase deficiency, discuss this with your doctor. 


Disclaimer: This is not medical advice. You and your physician will determine if and how you should take any medication prescribed to you following a medical consultation.

  1. Famvir (famciclovir) [prescribing information]. East Hanover, NJ: Novartis Pharmaceuticals Corporation; December 2018.

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