Birth Defects Not Caused by Some Antiviral Drugs

A higher risk of birth defects is not caused by using certain antiviral drugs, concludes a new study.

An analysis of data from Denmark found no associated increased risk of major birth defects for mothers who were exposed during the first trimester of pregnancy to the antiviral drugs acyclovir, valacyclovir, and famciclovir, often used to treat herpes simplex and herpes zoster infections.

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The prevalence of herpes simplex is high, and more than 1 percent of susceptible women acquire herpes simplex during the first trimester of pregnancy, with antiviral treatment indicated for a significant number of women in pregnancy.

"Although the safety of acyclovir, valacyclovir, and famciclovir in general has been well established, data on the use of these antivirals in early pregnancy are limited," the authors said.

Bjorn Pasternak, and Anders Hviid, M.Sc., Dr.Med.Sci., of Statens Serum Institut, Copenhagen, Denmark, conducted a registry-based study to assess associations between acyclovir, valacyclovir, and famciclovir use in the first trimester of pregnancy and major birth defects.

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The study included 837,795 live-born infants in Denmark from January 1996 to September 2008. Participants had no diagnoses of chromosomal aberrations, genetic syndromes, birth defect syndromes with known causes, or congenital viral infections.

Nationwide registries were used to ascertain individual-level information on dispensed antiviral drugs, birth defect diagnoses and potential confounders (factors that can influence outcomes).

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Among 1,804 pregnancies exposed to acyclovir, valacyclovir, or famciclovir at any time in the first trimester, 40 infants (2.2 percent) had a diagnosis of a major birth defect, compared with 19,920 of 835,991 infants (2.4 percent) among the unexposed pregnancies.

Adjusting for several variables, acyclovir, valacyclovir, or famciclovir exposure at any time in the first trimester was not associated with increased risk of major birth defects.

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First-trimester use of acyclovir, the most commonly prescribed antiviral, was not associated with major birth defects (32 cases among 1,561 exposed [2.0 percent] vs. 2.4 percent in the unexposed).

Neither valacyclovir (7 of 229 infants [3.1 percent]) nor famciclovir (1 of 26 infants [3.8 percent]) were associated with major birth defects, although use of famciclovir was uncommon.

Additional analyses revealed no associations between antiviral drug exposure and 13 different subgroups of birth defects, but the number of exposed cases in each subgroup was small.

The study appears in the August 25 issue of JAMA.

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