Famciclovir belongs to the family of medications known as antivirals.It is used to treat genital herpes and prevent recurring episodes of genital herpes. It is also used to treat shingles (a painful rash caused by some herpes viruses, also known as herpes zoster).

People infected with the human immunodeficiency virus (HIV), the virus that causes AIDS, may also be prescribed famciclovir to treat mucocutaneous herpes (herpes simplex outbreaks around the lips and mouth).

These infections are caused by viruses. Famciclovir prevents the virus from making DNA and copying itself, and so leads to lower levels of virus in the blood. It helps to prevent the virus from multiplying and spreading to nearby healthy cells, which helps healing.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

To treat shingles, the recommended adult dose of famciclovir is 500 mg taken 3 times daily for 7 days. Treatment is started within 72 hours of the onset of the rash.

To treat genital herpes, the recommended adult dose is 125 mg taken twice a day for 5 days. Start treatment during the prodromal period (the period during which early symptoms warn of a herpes flare-up) or as soon as you notice lesions.

To prevent recurrent episodes of genital herpes, the recommended dose is 250 mg taken twice a day for up to 1 year.

To treat mucocutaneous herpes, the recommended dose is 500 mg taken twice a day for 7 days.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

The tablets should be swallowed whole and may be taken with or without food. Famciclovir must be taken for the recommended duration of treatment, even if you are feeling better. This will help prevent the episode from flaring up and returning.

It is important to take this medication exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose (within 1 hour), skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature and keep it out of the reach of children.

Do not take famciclovir if you are allergic to famciclovir or to any of the ingredients of the medication.

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent. The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• diarrhea
• dizziness
• drowsiness
• headache
• nausea
• unusual tiredness or weakness
• vomiting

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• abdominal pain
• confusion
• fast or pounding heartbeat
• hallucinations
• purplish patches on skin
• signs of bleeding (e.g., nosebleeds, blood in urine, coughing blood, bleeding gums, unusual bruising or bleeding)
• symptoms of liver problems (e.g., abdominal tenderness, yellow eyes or skin, skin rash, itching, dark urine)
• skin rash

Stop taking the medication and seek immediate medical attention if any of the following occur:

• seizures
• symptoms of a serious allergic reaction (such as swelling of the face, lips, tongue, or throat; skin rash; hives; or difficulty breathing)
• signs of a severe skin reaction (e.g., a rash combined with fever or discomfort, a rash covering a large area of the body, a rash that spreads quickly, blistering, peeling)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Drowsiness/reduced alertness: This medication can cause drowsiness, dizziness, or confusion in rare cases. Do not drive or engage in other activities requiring alertness if the medication affects you in this way.

Genital herpes: Genital herpes is a sexually transmitted infection with an increased risk of passing it on to a sexual partner during acute episodes. It is not known if famciclovir will prevent transmission of the infection. If you are using this medication for this reason, avoid intercourse when lesions or symptoms are present (even if treatment with an antiviral has been started) in order to avoid infecting partners. Genital herpes can also be transmitted in the absence of symptoms.

Kidney or liver disorders: If you have liver disease, kidney disease, or reduced kidney function, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: It is not known if famciclovir passes into breast milk. If you are a breast-feeding mother and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of this medication for children and adolescents under the age of 18 years have not been established.

There may be an interaction between famciclovir and any of the following:

• cladribine
• varicella virus vaccine
• zoster vaccine

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.