Generic name: famciclovir
Brand name: Famvir
Dosage form: oral tablet (125 mg; 250 mg; 500 mg)
Drug class: Purine nucleosides

Medically reviewed by  A Ras MD.

What is famciclovir?

Famciclovir is a prescription medicine that is used to treat or prevent herpes infections. It is used to treat cold sores. Famciclovir is also used to treat shingles. Famciclovir may be given to you for other reasons.


The active ingredient in famciclovir tablets is famciclovir, USP, an orally administered prodrug of the antiviral agent penciclovir. Chemically, famciclovir, USP is known as 2-[2-(2-amino-9 H-purin-9-yl) ethyl]-1,3-propanediol diacetate. Its molecular formula is C 141954; its molecular weight is 321.3. It is a synthetic acyclic guanine derivative and has the following structure




Famciclovir, USP is a white to pale yellow solid. It is freely soluble in acetone and methanol, and sparingly soluble in ethanol and isopropanol. At 25°C famciclovir, USP is freely soluble (greater than 25% w/v) in water initially, but rapidly precipitates as the sparingly soluble (2% to 3% w/v) monohydrate. Famciclovir, USP is not hygroscopic below 85% relative humidity. Partition coefficients are: octanol/water (pH 4.8) P=1.09 and octanol/phosphate buffer (pH 7.4) P=2.08.

Famciclovir tablets contain 125 mg, 250 mg or 500 mg of famciclovir, USP, together with the following inactive ingredients: hydroxypropyl cellulose, lactose monohydrate, magnesium stearate and sodium starch glycolate. The tablets are coated with opadry white which contains hypromellose, polyethylene glycol, polysorbate 80 and titanium dioxide.

Before taking famciclovir, tell your doctor:

For all patients taking famciclovir:

  • If you are allergic to famciclovir; any part of this medicine; or any other drugs, foods, or substances. Tell your doctor about the allergy and what signs you had.
  • If you have a rare hereditary problem of galactose intolerance, Lapp lactase deficiency, or glucose-galactose malabsorption.


  • If your child is an infant. Do not give famciclovir to an infant.

This is not a list of all drugs or health problems that interact with famciclovir.

Tell your doctor and pharmacist about all of your drugs (prescription or OTC, natural products, vitamins) and health problems. You must check to make sure that it is safe for you to take famciclovir with all of your drugs and health problems. Do not start, stop, or change the dose of any drug without checking with your doctor.

What are some things I need to know or do while I take famciclovir?

  • Tell all of your health care providers that you take famciclovir. This includes your doctors, nurses, pharmacists, and dentists.
  • Avoid driving and doing other tasks or actions that call for you to be alert until you see how famciclovir affects you.
  • If you are taking famciclovir for cold sores, it will not cure cold sores. Talk with your doctor.
  • This medicine is not a cure for herpes infections. Talk with the doctor.
  • If you have genital herpes, famciclovir will not stop it from spreading. Do not have any kind of sex when you have sores or other signs of genital herpes. Genital herpes can also be spread if you do not have any signs. Do not have any kind of sex without using a latex or polyurethane condom. Talk with your doctor.
  • If you are 65 or older, use famciclovir with care. You could have more side effects.
  • Tell your doctor if you are pregnant or plan on getting pregnant. You will need to talk about the benefits and risks of using famciclovir while you are pregnant.
  • Tell your doctor if you are breast-feeding. You will need to talk about any risks to your baby.

How is famciclovir best taken?

Use famciclovir as ordered by your doctor. Read all information given to you. Follow all instructions closely.

  • Take with or without food.
  • Use as you have been told, even if your signs get better.
  • If you are taking famciclovir to treat an outbreak, take at the first signs of the outbreak.

What do I do if I miss a dose?

  • Take a missed dose as soon as you think about it.
  • If it is close to the time for your next dose, skip the missed dose and go back to your normal time.
  • Do not take 2 doses at the same time or extra doses.

What are the side effects of famciclovir that I need to call my doctor about immediately?

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

  • Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.

What are some other side effects of famciclovir?

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:

These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.

You may report side effects to the FDA at 1-800-332-1088. You may also report side effects at https://www.fda.gov/medwatch.

If overdose is suspected:

If you think there has been an overdose, call your poison control center or get medical care right away. Be ready to tell or show what was taken, how much, and when it happened.

How do I store and/or throw out famciclovir?

  • Store at room temperature.
  • Store in a dry place. Do not store in a bathroom.
  • Keep all drugs in a safe place. Keep all drugs out of the reach of children and pets.
  • Throw away unused or expired drugs. Do not flush down a toilet or pour down a drain unless you are told to do so. Check with your pharmacist if you have questions about the best way to throw out drugs. There may be drug take-back programs in your area.


Famciclovir Tablets 125 mg – 30’s Count Container Label


Imprint 93 8117 - famciclovir 125 mg

Famciclovir Tablets 250 mg – 30’s Count Container Label


Imprint 93 8118 - famciclovir 250 mg

Famciclovir Tablets 500 mg – 30’s Count Container Label


Imprint 93 8119 - famciclovir 500 mg