Famciclovir, Oral Tablet

Medically reviewed by University of Illinois-Chicago, Drug Information Group on May 3, 2017Written by University of Illinois-Chicago, Drug Information Group

Important warnings

  • Tiredness warning: Famciclovir can cause dizziness, confusion, or sleepiness. Don’t drive, use machinery, or do other dangerous activities until you know how this drug affects you.
  • Spread of herpes warning: Famciclovir is not a cure for herpes. This drug makes it harder for the herpes virus to grow and spread. This reduces the risk of spreading the disease to others. However, if you’re sexually active, there is always a risk of passing herpes to your partner. This can happen even if you’re taking famciclovir, or if you don’t have active herpes symptoms. To reduce the risk of spreading genital herpes to others, practice safer sex. For instance, use a condom made of latex or polyurethane.

What is famciclovir?

Famciclovir is a prescription drug. It comes in the form of a tablet you take by mouth.

Famciclovir is only available as a generic drug. Generic drugs usually cost less than brand-name drugs.

Why it's used

Famciclovir is used to treat outbreaks caused by herpes viruses. It can help treat:

  • oral herpes (cold sores on the mouth)
  • genital herpes (sores on the genitals)
  • shingles (a painful rash and blisters on the body)

Famciclovir is used for people with strong immune systems, as well as people who are infected with HIV. It should not be used to treat:

  • your first episode of genital herpes
  • herpes zoster infection of the eye
  • herpes in people with weakened immune systems not caused by HIV

Your race may affect how well this drug works in treating genital herpes. Your doctor can tell you more.

How it works

Famciclovir belongs to a class of drugs called antivirals. A class of drugs is a group of medications that work in a similar way. These drugs are often used to treat similar conditions.

Antivirals work by making viruses less active in your body. Famciclovir works against herpes simplex viruses 1 and 2 (HSV-1 and HSV-2). These viruses cause oral or genital herpes. Famciclovir also works against herpes zoster, the virus that causes shingles.

Famciclovir side effects

Famciclovir oral tablet doesn’t cause drowsiness, but it can cause other side effects.

More common side effects

The more common side effects of famciclovir can include:

  • headache
  • nausea

If these effects are mild, they may go away within a few days or a couple of weeks. If they’re more severe or don’t go away, talk to your doctor or pharmacist.

Serious side effects

Call your doctor right away if you have serious side effects. Call 911 if your symptoms feel life-threatening or if you think you’re having a medical emergency. Serious side effects and their symptoms can include the following:

  • Allergic reaction. Symptoms can include:
    • rash
    • hives
    • itchy, red, swollen, blistered, or peeling skin, with or without fever
    • wheezing
    • tightness in your chest or throat
    • swelling of your face, lips, tongue, or throat

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we can not guarantee that this information includes all possible side effects. This information is not a substitute for medical advice. Always discuss possible side effects with a healthcare provider who knows your medical history.

Famciclovir may interact with other medications

Famciclovir oral tablet can interact with other medications, vitamins, or herbs you may be taking. An interaction is when a substance changes the way a drug works. This can be harmful or prevent the drug from working well.

To help avoid interactions, your doctor should manage all of your medications carefully. Be sure to tell your doctor about all medications, vitamins, or herbs you’re taking. To find out how this drug might interact with something else you’re taking, talk to your doctor or pharmacist.

Examples of drugs that can cause interactions with famciclovir are listed below.

Drugs that increase the risk of side effects: Increased side effects from famciclovir

Taking famciclovir with certain medications raises your risk of side effects from famciclovir. This is because the amount of famciclovir in your body increases. Examples of these drugs include:

  • Probenecid and similar drugs. Increased side effects can include headache or nausea. Your doctor will probably not need to adjust your dosage of famciclovir. However, you should watch for side effects.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs interact differently in each person, we can not guarantee that this information includes all possible interactions. This information is not a substitute for medical advice. Always speak with your healthcare provider about possible interactions with all prescription drugs, vitamins, herbs and supplements, and over-the-counter drugs that you are taking.

Famciclovir warnings

This drug comes with several warnings.

Allergy warning

Famciclovir can cause a severe allergic reaction. Symptoms can include:

  • rash
  • hives
  • itchy, red, swollen, blistered, or peeling skin, with or without fever
  • trouble breathing
  • tightness in your chest or throat
  • swelling of your face, lips, tongue, or throat

If you develop these symptoms, call 911 or go to the nearest emergency room.

Don’t take this drug again if you’ve ever had an allergic reaction to it or to penciclovir cream. Taking it again could be fatal (cause death).

Warnings for people with certain health conditions

For people with lactose problems: Famciclovir contains lactose. If you have certain rare conditions that affect how well your body tolerates lactose, talk to your doctor before taking this drug. These conditions include not tolerating galactose or glucose-galactose. They also include having severely low lactase levels.

For people with kidney problems: If you have kidney problems or a history of kidney disease, you may not be able to clear this drug from your body well. This may increase the levels of famciclovir in your body and cause more side effects. This drug may also make your kidney disease worse. If you have kidney problems, your doctor will give you a lower dosage of this drug.

Warnings for other groups

For pregnant women: Famciclovir is a category B pregnancy drug. That means two things:

  1. Research in animals has not shown a risk to the fetus when the mother takes the drug.
  2. There aren’t enough studies done in humans to show if the drug poses a risk to the fetus.

Talk to your doctor if you’re pregnant or planning to become pregnant. Animal studies do not always predict the way humans would respond. Therefore, this drug should only be used in pregnancy if clearly needed.

For women who are breastfeeding: Famciclovir may pass into breast milk and may cause side effects in a child who is breastfed. Talk to your doctor if you breastfeed your child. You may need to decide whether to stop breastfeeding or stop taking this medication.

For seniors: The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, a higher amount of a drug stays in your body for a longer time. This raises your risk of side effects.

For children: This medication has not been approved for use in children. It should not be used in people younger than 18 years.

How to take famciclovir

All possible dosages and drug forms may not be included here. Your dosage, drug form, and how often you take the drug will depend on:

  • your age
  • the condition being treated
  • how severe your condition is
  • other medical conditions you have
  • how you react to the first dose

Drug form and strengths

Generic: Famciclovir

  • Form: oral tablet
  • Strengths: 125 mg, 250 mg, 500 mg

Dosage for oral herpes outbreaks

Adult dosage (ages 18 years and older)

  • Typical dosage: 1,500 mg taken as a single dose once per day.

Child dosage (ages 0–17 years)

This medication has not been approved for use in children. It should not be used in people younger than 18 years.

Dosage for genital herpes outbreaks

Adult dosage (ages 18 years and older)

  • Typical dosage for treatment: 1,000 mg taken twice per day for 1 day.
  • Typical dosage for long-term preventive care: 250 mg taken twice per day.

Child dosage (ages 0–17 years)

This medication has not been approved for use in children. It should not be used in people younger than 18 years.

Dosage for oral or genital herpes outbreaks in people with HIV

Adult dosage (ages 18 years and older)

  • Typical dosage: 500 mg taken twice per day for 7 days.

Child dosage (ages 0–17 years)

This medication has not been approved for use in children. It should not be used in people younger than 18 years.

Dosage for shingles outbreaks

Adult dosage (ages 18 years and older)

  • Typical dosage: 500 mg every 8 hours for 7 days.

Child dosage (ages 0–17 years)

This medication has not been approved for use in children. It should not be used in people younger than 18 years.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we can not guarantee that this list includes all possible dosages. This information is not a substitute for medical advice. Always speak with your doctor or pharmacist about dosages that are right for you.

Take as directed

Famciclovir is used for short-term treatment of oral or genital herpes, and shingles. It’s used for long-term treatment of genital herpes. This drug comes with serious risks if you don’t take it as prescribed.

If you stop taking the drug suddenly or don’t take it at all: Your herpes or shingles sores may not get better, or they may get worse.

If you miss doses or don’t take the drug on schedule: Your medication may not work as well or may stop working completely. For this drug to work well, a certain amount needs to be in your body at all times. If you miss too many doses over time, famciclovir may not work as well against the herpes viruses in your body. This is called resistance.

If you take too much: You could have dangerous levels of the drug in your body. Symptoms of an overdose of this drug can include:

  • headache
  • nausea
  • diarrhea

If you think you’ve taken too much of this drug, call your doctor or local poison control center. If your symptoms are severe, call 911 or go to the nearest emergency room right away.

What to do if you miss a dose: Take your dose as soon as you remember. But if you remember just a few hours before your next scheduled dose, take only one dose. Never try to catch up by taking two doses at once. This could result in dangerous side effects.

How to tell if the drug is working: You should have decreased pain and your herpes or shingles sores should get smaller or go away completely.

Important considerations for taking famciclovir

Keep these considerations in mind if your doctor prescribes famciclovir for you.

General

  • You can take famciclovir with or without food.
  • Take this drug at the time(s) recommended by your doctor.
  • You can cut or crush the tablet.

Storage

  • Store famciclovir at 77°F (25°C).
  • Keep this drug away from light.
  • Don’t store this medication in moist or damp areas, such as bathrooms.

Refills

A prescription for this medication is refillable. You should not need a new prescription for this medication to be refilled. Your doctor will write the number of refills authorized on your prescription.

Travel

When traveling with your medication:

  • Always carry your medication with you. When flying, never put it into a checked bag. Keep it in your carry-on bag.
  • Don’t worry about airport x-ray machines. They can’t harm your medication.
  • You may need to show airport staff the pharmacy label for your medication. Always carry the original prescription-labeled container with you.
  • Don’t put this medication in your car’s glove compartment or leave it in the car. Be sure to avoid doing this when the weather is very hot or very cold.

Self-management

When you should start taking this medication depends on the condition being treated.

  • Oral herpes: You should start taking famciclovir at the first sign of a cold sore on your mouth. Symptoms can include tingling, itching, burning, pain, or sores.
  • Genital herpes: You should start taking famciclovir at the first sign of sores on your genitals.
  • Shingles: You should start taking famciclovir as soon as possible after your doctor tells you that you have shingles. Be sure to start within 72 hours of when the rash first appears.

Be sure to finish all of this medication as prescribed, even if you start to feel better. Your symptoms may continue after you finish taking all of your famciclovir. This does not mean that you need more medication. After you finish taking a full course of famciclovir, it will continue to work in your body. Call your doctor if you’re not feeling better 3 to 7 days after finishing your prescription.

Availability

Not every pharmacy stocks this drug. When filling your prescription, be sure to call ahead to make sure your pharmacy carries it.

Prior authorization

Many insurance companies require a prior authorization for this drug. This means your doctor may need to get approval from your insurance company before your insurance company will pay for the prescription.

Are there any alternatives?

There are other drugs available to treat your condition. Some may be better suited for you than others. Talk to your doctor about other drug options that may work for you.

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up-to-date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or other healthcare professional before taking any medication. The drug information contained here in is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.

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