valacyclovir, Valtrex

GENERIC NAME: valacyclovir

BRAND NAME: Valtrex

DRUG CLASS AND MECHANISM: 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 (Zovirax) 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.

PRESCRIPTION: yes

GENERIC AVAILABLE: yes

PREPARATIONS: Caplets (blue): 500 mg

STORAGE: Valacyclovir should be kept between 2 and 30 C (36 and 86 F).

PRESCRIBED FOR: Valacyclovir is used to treat infections with herpes zoster (shingles), herpes simplex genitalis (genital herpes), and herpes labialis (cold sores).

DOSING: 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.

DRUG INTERACTIONS: Probenecid (Benemid) and cimetidine (Tagamet) may reduce the kidney's clearance of valacyclovir, leading to higher concentrations in the blood. This may lead to side effects of valacyclovir.

PREGNANCY: Valacyclovir showed no effects on the fetus in animal studies, however, there has been no adequate evaluation of valacyclovir or (acyclovir) in pregnant women. The incidence of birth defects in women taking acyclovir is about the same as in the general population. Valacyclovir should only be used during pregnancy when the benefits to the mother outweigh risks to the fetus.

NURSING MOTHERS: It is not known whether valacyclovir is excreted into breast milk. It is known, however, that among women taking acyclovir, concentrations of acyclovir in breast milk are about four times higher than in the mother's blood. The safety of valacyclovir in breast-feeding infants has not been established. Methods other than breast feeding should be considered if Valacyclovir must be taken while nursing.

SIDE EFFECTS: 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.

Reference: FDA Prescribing Information

Last Editorial Review: 12/14/2010

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