Medically Reviewed on 2/28/2023

Generic Name: acyclovir

Brand Name: Zovirax, Sitavig

Drug Class: Antivirals, VZV, Antivirals, HSV, Antivirals, Other

What is acyclovir, and what is it used for?

Acyclovir is an antiviral drug, a synthetic nucleoside analogue, that has inhibitory activity (interferes with viral replication) against the herpes viruses, including herpes simplex 1 and 2 (cold sores and genital herpes), varicella-zoster (shingles and chickenpox), and Epstein-Barr virus (mononucleosis).

Viruses take over living cells and reproduce themselves, often at the expense of the host cell. The acyclovir is converted to an active form by the virus itself, and the virus then uses the active form of acyclovir rather than the nucleoside it normally uses to manufacture DNA, a critical component of viral replication. Incorporation of active acyclovir into new viral DNA stops the production of the DNA. Virally infected cells absorb more acyclovir than normal cells and convert more of it to the active form, which prolongs its antiviral activity.

Acyclovir is used to treat the following conditions:

The FDA approved acyclovir in March 1982.

What are the side effects of acyclovir?

The most common side effects are

Other reported side effects include:


Is genital herpes contagious? See Answer

What is the dosage for acyclovir?

Acyclovir may be taken with or without food.

  • Adult oral doses for treating genital herpes are 200 mg every 4 hours (5 times daily) for 7-10 days or 400 mg three times daily for 5-10 days.
  • Herpes Zoster (shingles) is treated with 800 mg every 4 hours (5 times daily) for 7 to 10 days.
  • The dose for treating chicken pox is 800 mg 4 times daily. The usual adult intravenous dose is 5-10 mg/kg every 8 hours for 7-10 days.

Which drugs interact with acyclovir?

Pregnancy and breastfeeding

  • There are no adequate studies of acyclovir in pregnant women. In a patient registry of women who used acyclovir during the first trimester, the rate of birth defects was similar to the rate of birth defects in the general population.
  • Acyclovir is excreted in breast milk, and a significant amount may be transferred to the infant.

What else should I know about acyclovir?

What preparations of acyclovir are available?

  • Capsules: 200 mg.
  • Tablets: 400 and 800 mg.
  • Suspension: 200 mg/5 ml.
  • Injection: 50 mg/ml.
  • Powder for injection: 500 and 1000 mg.
  • Ointment: 5%.

How should I keep acyclovir stored?
  • Acyclovir should be stored at room temperature, between 15 C 25 C (59 F to 77 F).


Acyclovir is an antiviral drug prescribed to treat genital herpes, shingles, and chickenpox. The most common side effects are nausea, vomiting, diarrhea, and headache. Other reported side effects include agitation, confusion, rash, anemia, hypersensitivity reactions, seizures, agitation, confusion, anemia, hepatitis, and muscle pain. Consult your doctor if pregnant or breastfeeding.

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See more info: acyclovir on RxList
Medically Reviewed on 2/28/2023
FDA Prescribing Information