Brand Name - Famvir

  • Type of Drug: Antiviral
  • Prescribed for: Shingles (herpes zoster infections)

General Information

Famciclovir is the second antiviral product (after Acyclovir) to be approved for treatment of herpes zoster infection. Famciclovir also works against herpes simplex virus infections. After it is absorbed into the body, Famciclovir is converted into Penciclovir, which works against shingles by interfering with basic reproductive DNA in the viruses. Penciclovir does not work on DNA in uninfected body cells. Penciclovir is broken down in the liver and eliminated from the body through the kidneys.

Cautions and Warnings

People sensitive or allergic to Famciclovir should not take this drug.
People with a loss of kidney function should have their dosage adjusted accordingly. Severe liver disease also calls for a reduction in daily Famciclovir dosage.
Lab animals receiving 1 ½ times the maximum dosage of Famciclovir developed tumors and testicular toxicity (abnormal or reduced numbers of sperm). The implication of these findings for people is not known.

Possible Side Effects

In preliminary studies of this drug, side effects were about equal in people who received Famciclovir and those who took an inactive placebo.

  • Most common: headache, nausea, and diarrhea.
  • Less common: fever, fatigue, pain, vomiting, constipation, loss of appetite, dizziness, tingling in the hands or feet, sleepiness, sore throat, sinus irritation, itching, and signs of shingles.
  • Rare: chills, abdominal pains, and back or joint pains.

Drug Interactions

• Probenecid interferes with the elimination of Penciclovir from the body, possibly leading to higher than expected levels of Penciclovir in the blood.
• People who took both Famciclovir and Digoxin together had more Digoxin in their blood than those who did not take Famciclovir.

Food Interactions

This drug may be taken without regard to food or meals.

Usual Dose

Adult (age 18 and older): 500 mg every 8 hours for 1 week. People with reduced kidney function may take it as infrequently as once a day.
Child (under age 18): not recommended.


There is little information available about the effects of Famciclovir overdose. Overdose victims should be taken to a hospital emergency room for treatment. ALWAYS bring the medicine bottle with you.

Special Information

This drug should be started as soon as shingles are diagnosed. Be sure to complete the full week of treatment to get the maximum benefit from this medicine.

Call your doctor if any unusual side effects develop or if your side effects become particularly intolerable.

If you forget a dose of Famciclovir, take it as soon as you remember. If it is almost time for your next dose, skip the forgotten dose. Do not take a double dose. Call your doctor if you forget to take more than 2 doses in a row.

Special Populations

Famciclovir should be taken by a pregnant woman only if it is absolutely necessary and the possible benefits outweigh the possible risk to the developing baby.
In animal studies, Penciclovir passes into breast milk in high concentrations, but it is not known if this happens in people. Nursing mothers who must take this medicine should, bottle-feed their babies.

Older adults have more active Penciclovir in their blood after taking Famciclovir than younger people and should have their dosage adjusted according to kidney function.