Famvir (Famciclovir)

How does it work?

Famvir tablets contain the active ingredient famciclovir, which is an antiviral medicine used to treat infections with herpes viruses. (Famciclovir is also available without a brand name, ie as the generic medicine.)

The herpes viruses include the viruses that cause genital herpes (herpes simplex types 1 and 2) and the virus that causes chickenpox and shingles (varicella zoster). Famciclovir works by stopping these herpes viruses from reproducing and infecting more cells in the body.

Once inside the body famciclovir is converted into another antiviral medicine called penciclovir. Penciclovir is converted to a more active form inside cells of the body that are infected with herpes viruses. The activated penciclovir then works by blocking the action of a viral enzyme called DNA polymerase.

The herpes viruses need the DNA polymerase enzyme to copy their genetic material from RNA to DNA. This process is necessary for the viruses to multiply and continue to survive. By blocking the action of DNA polymerase, penciclovir prevents the herpes viruses from multiplying. This controls the infection and helps the immune system to deal with it.

This medicine is taken by mouth to treat herpes infections that cause shingles. It is also taken by mouth to treat genital herpes, and to prevent this infection coming back in people who suffer recurrent infections. Famciclovir is also valuable for preventing herpes simplex infections in people whose immune systems are suppressed and therefore cannot fight off infection, either due to disease, eg HIV and AIDS, or medical treatment, eg chemotherapy, high-dose corticosteroids, bone marrow transplant.

What is it used for?

  • Shingles (herpes zoster).
  • Genital herpes (herpes simplex).
  • Preventing recurrence of genital herpes.
  • Preventing herpes simplex infections in people whose immune systems are impaired, eg due to disease or treatment.


  • Take this medicine at regular intervals as prescribed. Complete the prescribed course unless otherwise directed by your doctor.
  • Genital herpes is a sexually transmitted disease. The risk of passing the infection on to your sexual partner is greatest when you have active symptoms of the infection. There is still a risk of passing the infection on if you use condoms, and even if you are taking this medicine to help control the infection. It is therefore important that you avoid having sex while you have symptoms, even if you are taking this medicine to treat it.

Use with caution in

  • Decreased kidney function.
  • Uncontrolled chronic liver disease.

Not to be used in

  • Allergy to penciclovir.
  • This medicine is not recommended for children.
  • People with rare hereditary problems of galactose intolerance, a severe lactase deficiency or glucose-galactose malabsorption should not take Famvir 125mg or 250mg tablets, as these strength tablets contain lactose.

This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

Pregnancy and breastfeeding

Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.

  • The safety of this medicine for use during pregnancy has not been established. It should be used with caution during pregnancy, and only if the expected benefit to the mother is greater than any possible risk to the developing baby. Seek medical advice from your doctor.
  • It is not known if this medicine passes into breast milk. It should be used with caution in women who are breastfeeding, and only if the expected benefit to the mother is greater than any possible risk to the nursing infant. Seek medical advice from your doctor.

Label warnings

  • Take at regular intervals. Complete the prescribed course unless otherwise directed.

Side effects

Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Just because a side effect is stated here does not mean that all people using this medicine will experience that or any side effect.

Rare (affect between 1 in 1000 and 1 in 10,000 people)

  • Headache.
  • Feeling sick.
  • Confusion (primarily in elderly people).

Very rare (affect less than 1 in 10,000 people)

  • Vomiting.
  • Dizziness.
  • Sleepiness (primarily in elderly people).
  • Rash or itching.
  • False perceptions of things that are not really there (hallucinations).
  • Yellowing of the skin or whites of the eyes (jaundice).
  • Abnormal liver function.

Unknown frequency

  • Serious allergic skin reactions, such as severe blistering of the skin and/or lips, eyes, mouth, nasal passages or genitals.
  • Decreased number of platelets (cells that help the blood to clot) in the blood. This may cause unexplained bruising, reddish or purplish patches on the skin or nosebleeds.

The side effects listed above may not include all of the side effects reported by the medicine's manufacturer.For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

How can this medicine affect other medicines?

It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while taking this one, to ensure that the combination is safe.

Probenecid may decrease the excretion of famciclovir by the kidneys, leading to higher levels of famciclovir in the bloodstream.

Other medicines containing the same active ingredient

Famciclovir tablets are also available without a brand name, ie as the generic medicine.