valacyclovir, Valtrex

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GENERIC NAME: valacyclovir


DRUG CLASS AND MECHANISM: Valacyclovir is an oral antiviral drug which is active against the herpes viruses. It is used to treat infections with shingles (herpes zoster), genital herpes (herpes simplex genitalis), and cold sores (herpes labialis). It belongs to a class of drugs called nucleoside analogs that mimic one of the building blocks of DNA. It stops the spread of herpes virus in the body by preventing the replication of viral DNA that is necessary for viruses to multiply. Other drugs in the same class include acyclovir (Zovirax) and famciclovir (Famvir). Valacyclovir is actually a "prodrug," in that it is not active itself. Rather, it is converted to acyclovirin 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.



PREPARATIONS: Tablets : 500, 1000 mg

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

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

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. The dose for chickenpox is 20 mg/kg 3 times daily for 5 days (maximum dose is 1000 mg 3 times daily) and treatment should start at the earliest sign or symptom.

For the treatment of an initial episode of genital herpes, the usual dose is 1 gram (1000 mg) twice daily for 10 days. For the treatment of recurrent genital herpes, the usual dose is 500 mg twice daily for 3 days. For best results, treatment should be initiated within 12 hours of the start of symptoms.

The dose for cold sores is 2000 mg (2 grams) every 12 hours for 1 day.

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 breastfeeding infants has not been established. Methods other than breastfeeding 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, vomiting, abdominal pain, cold symptoms, increased liver enzymes, and reduction of white blood cells. Less common side effects are diarrhea, joint pain, and dizziness.

Reference: FDA Prescribing Information

Medically Reviewed by a Doctor on 8/8/2013

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