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Famciclovir is an antiviral drug which is active against the Herpes viruses including herpes simplex 1 and 2 cold sores and genital herpes and varicella-zoster shingles and chicken pox. It inhibits the replication of viral DNA that is necessary in order for viruses to reproduce themselves. Famciclovir is actually a prodrug in that it is not active directly against viruses. Instead famciclovir is converted to penciclovir in the body and it is the penciclovir that is active against the viruses. Penciclovir also is available as a topical and intravenous medication. Famciclovir is active against the same viruses as acyclovir but has a longer duration of action. Therefore it can be taken fewer times each day. Famciclovir was approved for use by the FDA in 1994.

Famciclovir may be taken with or without food. Penciclovir the active metabolite of famciclovir is excreted mainly by the kidney and dosages of famciclovir need to be reduced in patients with kidney dysfunction.

The most common side effects associated with the use of famciclovir are headache fatigue nausea and vomiting. Less common side effects include fever pain shaking chills constipation loss of appetite abdominal pain back pain joint pain dizziness tingling of the extremities tiredness sore throat sinus congestion and itching.

Probenecid Benemid may reduce the kidneys clearance of penciclovir leading to higher concentrations of penciclovir in the blood. This may lead to side effects of penciclovir. Using famciclovir with digoxin Lanoxin may result in an increase in the concentration of digoxin in the blood. This may lead to side effects of digoxin.

Famciclovir is used to treat the first episode of genital herpes and to treat patients with recurrent more than 6 episodes per year severe genital herpes. Famciclovir reduces the pain and the number of sores with the first episode and decreases the frequency and severity of episodes in individuals with recurrent episodes. In the treatment of shingles famciclovir reduces pain shortens the time in which sores heal and limits the spread of virus and the formation of new sores. Famciclovir can be used to treat chicken pox to reduce healing time limit the number of sores pox and reduce fever if used within the first 24 hours after the onset of the disease.

Famciclovir should be kept between 2° and 30°C 36-86° F.