Antiviral medicines for genital herpes


Generic Name Brand Name
acyclovir Zovirax
famciclovir Famvir
valacyclovir Valtrex

Acyclovir, famciclovir, and valacyclovir are antiviral medicines used to treat genital herpes. All are effective, but because valacyclovir and famciclovir are absorbed better by the stomach, they can be taken less often than acyclovir. Antiviral medicines are usually taken by mouth (orally), but they are sometimes given intravenously (IV) in severe genital herpes outbreaks or herpes in newborns.

The topical form of acyclovir (Zovirax ointment) offers little benefit in the treatment of genital herpes and is not recommended.

How It Works

Antiviral medicines stop the growth of the herpes simplex virus (HSV).

Why It Is Used

Antiviral medicines may be given to:

  • People who are having a primary outbreak of genital herpes.
  • People who have frequent (about 6 or more a year) recurrent outbreaks of genital herpes.
  • People who want to decrease the length and severity of their recurrent outbreaks.
  • People who want to decrease the possibility of unintentionally transmitting the virus. Genital herpes is more likely to be transmitted during the first year of infection, even though a person may not have symptoms of a genital herpes outbreak.
  • Pregnant women who are having a primary outbreak of genital herpes.
  • Women in the last 4 weeks of their pregnancy who are having frequent recurrent outbreaks.
  • People who have impaired immune systems and recurrent outbreaks.

How Well It Works

Initial outbreak

Antiviral medicines may significantly reduce the severity of an outbreak of genital herpes and decrease the time it takes an outbreak to heal. The medicine also decreases the number of days of painful symptoms. And for some people, this medicine decreases the number of days you can spread the virus.1

The amount and how often you take antivirals depends on the specific antiviral and whether you are taking them for a primary outbreak, recurrent outbreak, or for suppressive therapy.

Recurrent outbreaks

Antiviral medicine is most effective if it is taken when you first notice the prodromal symptoms (tingling and pain) of a recurrent genital herpes outbreak and if it is taken for the next 5 to 7 days or until symptoms go away.

Some people with frequent recurrent outbreaks (more than 6 recurrences a year) take antiviral medicine every day (suppressive therapy) to help reduce the frequency and duration of recurrent outbreaks. Antiviral medicine can reduce the number of outbreaks by 70% to 80%.2

Suppressive therapy

Research shows that acyclovir has been safely used long-term for as long as 6 years and valacyclovir or famciclovir for 1 year.2

Research shows that an HSV-infected person in a heterosexual, single-partner (monogamous) relationship who takes valacyclovir daily in the doses used for suppressive therapy to prevent recurrent outbreaks reduces the risk of infecting his or her partner.3 Other antiviral medicines may also reduce transmission but further study is needed.

Treatment during pregnancy

The CDC has published guidelines about the use of antiviral medicines in pregnancy.2

  • Oral acyclovir may be given to pregnant women for a primary HSV infection or for severe recurrent outbreaks.
  • Oral acyclovir may be given to pregnant women at any time during the pregnancy, including the first trimester.
  • Acyclovir may be given intravenously (IV) to pregnant women with severe HSV infection.
  • Acyclovir may decrease the frequency of recurrent outbreaks in pregnant women close to delivery, thereby reducing the possibility of needing a cesarean section at the time of delivery.

If a genital herpes blister or sore is present at the time of labor and delivery, a cesarean section is usually done. A cesarean section may be recommended if a woman suspects she has symptoms of an impending outbreak, such as tingling or pain (prodromal symptoms). For women who have recurrent outbreaks, acyclovir used in the last 4 weeks of pregnancy may reduce the need for a cesarean section by reducing the risk of an outbreak at the time of delivery.

People with human immunodeficiency virus (HIV) should talk with their doctors for advice about these medicines. Depending on the stage of their illness, they may need higher doses or longer treatment time with antiviral medicines.

Side Effects

Side effects include:

  • Headache, lightheadedness, or feelings of general illness (malaise).
  • Nausea and vomiting.
  • Decreased appetite or abdominal pain.
  • Joint pain.
  • Diarrhea or constipation (rare).
  • Kidney problems in people who receive large doses of intravenous acyclovir (rare).

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Treatment with antiviral medicines may decrease the length of time a person is able to transmit the genital herpes virus to others. Abstain from sexual contact while you are being treated for symptoms of an outbreak of genital herpes.

The effectiveness of the antiviral medicines acyclovir (Zovirax), famciclovir (Famvir), and valacyclovir (Valtrex) is equal in studies done so far.

Acyclovir is available in a generic form, which is less expensive. Taking any antiviral medicine on a daily basis may be expensive.

Taking antiviral medicine for a primary genital herpes outbreak does not keep genital herpes outbreaks from recurring.

People taking antiviral medicine every day (suppressive therapy) may want to talk to their doctor about whether they should stop taking the medicine for a short period each year. This can help determine whether genital herpes outbreaks recur as frequently. They can then decide whether they need to continue taking medicine. People who have six or more outbreaks a year may benefit from taking antiviral medicine every day.

People who have problems with their kidneys need to take a lower dose of acyclovir (Zovirax).

In rare cases, the genital herpes virus has developed a resistance to some antiviral medicines. This is more likely to occur in people who have impaired immune systems and who have taken antiviral medicines for an extended period. Other antiviral medicines are available in these cases, but they must be given intravenously (IV) and may not be as safe.

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  1. Jungmann E (2007). Genital herpes, search date August 2006. Online version of BMJ Clinical Evidence:
  2. U.S. Department of Health and Human Services (2006). Genital HSV infections. Sexually Transmitted Diseases Treatment Guidelines 2006 (CDC Publication Vol. 55, No. RR-11), pp. 16–20. Atlanta: U.S. Department of Health and Human Services. Available online:
  3. Corey L, et al. (2004). Once-daily valacyclovir to reduce the risk of transmissioin of genital herpes. New England Journal of Medicine, 350(1): 11–20.

Last Updated: January 13, 2009

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