Valacyclovir is an oral antiviral drug which is active against the Herpes viruses. It is used to treat infections with herpes zoster shingles herpes simplex genitalis genital herpes and herpes labialis cold sores. Valacyclovir inhibits the replication of viral DNA which is necessary for viruses to reproduce themselves. Valacyclovir is actually a prodrug in that it is not active itself. Rather it is converted to acyclovir in the body and it is the acyclovir that is active against the viruses. Acyclovir itself is available as a topical oral and intravenous medication. Valacyclovir therefore is active against the same viruses as acyclovir but valacyclovir has a longer duration of action than acyclovir and therefore can be taken fewer times each day. Valacyclovir was approved for use by the FDA in 1995.

Valacyclovir may be taken with or without food. Dosages need to be reduced in patients with kidney disease. For the treatment of herpes zoster shingles the usual dose is 1 gm three times a day for 7 days. Treatment should begin at the first symptom and is most effective if started within 48 hours of the onset of rash.

For the treatment of an initial episode of herpes the usual dose is 1 gm twice daily for 10 days. For the treatment of recurrent herpes the usual dose is 500 mg twice daily for 5 days. For best results treatment should be initiated within 12 hours of the start of symptoms.

The side effect profile of valacyclovir is similar to that of acyclovir. The most commonly reported side effects are headache nausea and vomiting. Less common side effects are diarrhea abdominal pain and dizziness.

Probenecid Benemid and cimetidine Tagamet may reduce the kidneys clearance of Valacyclovir leading to higher concentrations in the blood. This may lead to side effects of valacyclovir.

Valacyclovir is used to treat infections with herpes zoster shingles herpes simplex genitalis genital herpes and herpes labialis cold sores.

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