A study of birth records in Denmark shows no increase in birth defects among children born to mothers who received the antiviral drugs acyclovir, valacyclovir and famciclovir during the first trimester of pregnancy, researchers said Monday. The drugs are often used to treat herpes simplex and herpes zoster infections.
About two out of every 1,000 American women are exposed to the drugs during the first trimester, researchers from the National Institutes of Child Health and Human Development said in an editorial accompanying the report in the Journal of the American Medical Assn. That means about 15,000 fetuses are exposed to the drugs each year, even though there is little information available about the drugs' teratogenicity, so the study is a welcome addition to the literature.
Dr. Bjorn Pasternak and Dr. Anders Hviid of Statens Serum Institut in Copenhagen studied records for 837,795 babies born in Denmark from January 1996 to September 2008, cross-referencing them to registries of prescriptions for drugs and for birth defects. They did not include birth defects caused by chromosomal abnormalities, known genetic conditions and congenital virus infections.
Among the 1,804 pregnancies exposed to one of the three antiviral agents, there were 40 infants (2.2%) with a major birth defect, compared with 19,920 of 835,991 (2.4%) of those not exposed to the drugs. The majority of the exposures involved acyclovir, and it proved to be safe. There were insufficient cases with the other two drugs to firmly show lack of effect, but the results were encouraging.
"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 authors wrote. "Consequently, it has immediate clinical implications and may support informed decisions on safety when prescribing antivirals for herpes infections in early pregnancy. Acyclovir is the most extensively documented antiviral and should therefore be the drug of choice in early pregnancy."
The study leaves some questions unanswered, however. It was not large enough to show whether any of the drugs might be linked to a rare birth defect. Moreover, other studies have shown that many people prescribed drugs, especially pregnant women, do not take them, because of fears of side effects. The authors had no way to determine whether the women in the study actually took the antivirals. Also, the registries include only birth defects identified during the first year of life, and could have overlooked those that developed later.
-- Thomas H. Maugh II / Los Angeles Times