Herpes Drugs May Be Safe in Early Pregnancy

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Certain Antivirals in the First Trimester Do Not Appear to Increase Risk of Birth Defects, Study Finds

By Kelli Miller Stacy
WebMD Health News

Reviewed By Laura J. Martin, MD

Aug. 24, 2010 -- Taking certain antiviral medications for herpes infections during the first three months of pregnancy does not increase a child's risk of major birth defects, researchers report in this week's issue of the Journal of the American Medical Association.

The antiviral drugs acyclovir, valacyclovir, and famciclovir are often prescribed to treat herpes viral infections, such as herpes simplex virus (HSV). More than one in five pregnant women have antibodies in their blood to HSV, indicating a past or present infection.

Herpes antiviral medications are also used to treat herpes zoster infections, commonly known as shingles.

Until now, information about the safety of these antivirals during pregnancy has been limited, according to background information in the journal article. The medications are listed as category B by the FDA. Category B means adequate studies on pregnant women are lacking but animal studies have shown the medicine is safe during pregnancy, or human studies showed it was safe during pregnancy but animal studies offered conflicting evidence.

The Study

The new study suggests that pregnant women may be able to take some of these drugs without fear of harming their developing baby, at least during the first trimester. Researchers in Copenhagen, Denmark, looked at live birth records from more than 800,000 infants between January 1996 to September 2008, noting the link between acyclovir, valacyclovir, and famciclovir use in the first trimester of pregnancy and major birth defects. Participants had no medical history of chromosome or genetic problems or viral infections at birth. The study team also adjusted for other factors known to influence outcome.

"Our study, to our knowledge the largest of its kind, found no significant association between first-trimester exposure to antiherpetic antiviral drugs and major birth defects," the study authors write in the journal report. "Acyclovir is the most extensively documented antiviral and should therefore be the drug of choice in early pregnancy."

The study authors warn that their analysis regarding famciclovir was based on a small number of pregnancies and should "not be viewed as evidence of safety of this drug." Data on valacyclovir also remains insufficient, they say. The team encourages continued research to study the link between these medications and miscarriage and preterm labor, and their safety during breastfeeding.

SOURCES: News release, American Medical Association.

Pasternak, B. Journal of the American Medical Association, Aug. 25, 2010; vol 304: pp 859-866.

Mills, J. Journal of the American Medical Association, Aug. 25, 2010; vol 304: pp 905-906.

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