Medically Reviewed on 10/31/2022

Brand Name: Valtrex

Generic Name: valacyclovir

Drug Class: Antivirals, HSV, Antivirals, Other

What is valacyclovir (Valtrex)? What are its uses?

Valacyclovir (Valtrex) is an oral antiviral drug that is active against herpes viruses. It is used to treat infections with:

What are the side effects of valacyclovir (Valtrex)?

The side effect profile of valacyclovir (Valtrex) is similar to that of acyclovir (Zovirax).

Common side effects are:

Other important side effects are:

More serious side effects include central nervous system side effects which are more likely to happen in the elderly, for example:

What is the dosage for valacyclovir (Valtrex)?

  •  Valacyclovir (Valtrex) may be taken with or without food.
  • In people with kidney disease, doses need to be reduced.
  • 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 the 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.

Which drugs or supplements interact with valacyclovir (Valtrex)?

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


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Is valacyclovir (Valtrex) safe to use during pregnancy or while breastfeeding?

  • Valtrex 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. Valtrex should only be used during pregnancy when the benefits to the mother outweigh risks to the fetus.
  • It is not known whether Valtrex 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.

How does valacyclovir (Valtrex) work (mechanism of action)?

Valtrex belongs to a class of drugs called nucleoside analogs that mimic one of the building blocks of DNA. It stops the spread of the 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 a "prodrug," in that it is not active itself. Rather, it is converted to acyclovirin 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.

The FDA approved valacyclovir in 1995.

What else should I know about valacyclovir (Valtrex)?

  • Valacyclovir is available as tablets of 500 and 1000 mg
  • Valtrex should be kept stored between 2 C and 30 C (36 F and 86 F).
  • Valacyclovir is available in generic form. You need a prescription from your doctor for it.


Valacyclovir (Valtrex) is an antiviral drug prescribed for the treatment of herpes viruses such as shingles, genital herpes, and cold sores. Side effects include abdominal pain, diarrhea, dizziness, nausea, vomiting, and headache. Drug interactions, warnings and precautions, and pregnancy and breastfeeding safety information should be reviewed before taking any medication.

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See more info: valacyclovir on RxList
Medically Reviewed on 10/31/2022
Medically reviewed by John P. Cunha, DO, FACOEP; Board Certified Emergency Medicine


FDA Prescribing Information