Famciclovir - how long does it take to work?

Famciclovir usually acts fast but the speed of efficacy will depend on when you started your treatment…


Famciclovir (Famvir) is an antiviral drug prescribed to treat shingles, outbreaks of genital herpes and fever blisters or cold sores.


What is Famciclovir?

Infections caused by the herpes simplex virus (HSV) including genital herpes (HSV-2) and cold sores (HSV-1) and those caused by herpes zoster (shingles) are very common.

Famciclovir is prescribed at the first sign of a herpes or shingles flare-up to prevent the herpes virus from spreading. It also helps to speed up recovery and heal open sores and blisters.

Although famciclovir is not a herpes cure, it can help to reduce pain, discomfort, and itching.

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The correct dosage will depend on the type of herpes virus and the severity of your symptoms. But you should take famciclovir as soon as symptoms occur, as fast treatment helps to speed up the recovery process.

To treat shingles:

  • Take 500 mg of famciclovir 3 times a day for 7 days

To treat genital herpes:

  • Take 250 mg of famciclovir 3 times a day for 5 days

To treat cold sores and fever blisters:

  • Take 1.5 g of famciclovir once


Can you take Famciclovir daily?

Yes, famciclovir can be taken daily for herpes suppression, to lower the risk of genital herpes or shingles outbreaks.  

You may be prescribed 250 mg of the medicine to be taken twice a day for 12 months.

Suppression therapy is also advised during pregnancy to avoid viral shedding and transmission of HSV infection to the baby.

Studies have shown that famciclovir is safe when administered over a period of 1 year. Speak to your doctor if you plan to take famciclovir for longer than 52 weeks.


How long does Famciclovir take to work?

Famvir acts rapidly if taken at the first signs of an outbreak (within 48 hours). You should usually notice an improvement in symptoms after 48 hours. If your immune system is weak, it may take a little longer for your body to heal.

Whether famciclovir provides the same level of efficacy if taken later than 48 hours after the first signs of a genital herpes outbreak or the onset of shingles is not well understood. 

Open sores and blisters usually take 2 to 4 weeks to heal fully if untreated.

If you’ve previously been prescribed acyclovir and are swapping to famciclovir, the dosage may appear a little different. Famciclovir has a much longer half-life (10x) than acyclovir, which means that you may end up taking fewer pills.

Famciclovir can take longer to work during your first HSV-1, HSV-2 or shingles infection.

When taking the medication during recurring outbreaks, you may notice symptoms subsiding much faster.


How long does it take for Famciclovir to work for shingles?

If taken within 72 hours after noticing shingles symptoms (such as skin rash, pain, headache, itching and burning, and fever), you should begin to feel better within 72 hours.


How long does Famciclovir take to work for cold sores?

The famciclovir dose for cold sores usually involves taking the medication once after sores appear. If your sores have already formed a crust, do not take famciclovir as that’s a sign of sores healing.

Associated symptoms such as fever, pain, and headaches may disappear within a few days after taking famciclovir, but cold sores usually take 2 to 4 weeks to heal completely.


How long after taking Famciclovir are you contagious?

Carriers of HSV are always contagious. But studies have shown that famciclovir can decrease viral shedding and minimize the risk of spreading HSV-2.

There is no cure for herpes simplex, so carriers must take extra precaution during sexual intercourse such as wearing a condom and dental dam and avoid skin or genital contact during times of an active breakout.


How long does Famciclovir stay in your system?

Famciclovir has a half-life of 10 hours in HSV-1 infected cells and 20 hours in HSV-2 infected cells. In cells infected with herpes zoster, the drug has a half-life of 9 to 14 hours.

The long half-life of the medicine is a consideration for seniors. Kidney function in older adults can be slower which means that the drug will stay in the body for longer.


Reviewed by Dr Roy Kedem, MD

Information last reviewed 07/12/21

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