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Antiviral exposure not linked to birth defects
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Antiviral medications used to treat herpes infections appear to have no effect on the development of major birth defects in infants exposed to the drugs during the first trimester, according to recently published data.
Researchers from the Statens Serum Institute of Copenhagen, Denmark, said incidence of herpes simplex and herpes zoster is high, and many women acquire these infections at the beginning of pregnancies. "Given this background, antiviral treatment will be indicated for a significant number of women in pregnancy," they wrote.
To evaluate the risk of birth defects for pregnant women taking three antiviral drugs commonly prescribed for treatment of herpes infections — acyclovir, valacyclovir and famciclovir — the researchers conducted a population-based historical cohort study of infants born live in Denmark from January 1996 to September 2008.
The study population was composed of 837,795 infants, 34,787 of whom were multiple births, with no evidence of chromosomal aberrations, genetic syndromes, birth defect syndromes with known causes or congenital viral infections.
The researchers used data from the nationwide Medical Birth Register and Prescription Drug Register to determine individual characteristics of each birth in the cohort and the possibility of antiviral exposure during pregnancy. They also searched the National Patient Register to identify infants diagnosed with major birth defects within the first year of life.
Of the 1,804 pregnancies with first-trimester exposure to the three antivirals, 2.2% of infants were diagnosed with major birth defects compared with 2.4% among those without antiviral exposure (prevalence OR=0.93; 95% CI, 0.68-1.27).
After adjusting for variables, data did not indicate any connection between increased risk for major birth defects and exposure to acyclovir, valacyclovir or famciclovir during the first trimester.
Individual analysis suggested that acyclovir had no association with major birth defects, with only 2% of infants having major birth defects among the 1,561 with first-trimester exposure compared with 2.4% among unexposed infants (adjusted prevalence OR=0.82; 95% CI, 0.57-1.17).
Valacyclovir was also not statistically linked to major birth defects, with 3.1% of the 229 infants with first-trimester exposure to the medication having major birth defects (adjusted prevalence OR=1.21; 95% CI, 0.56-2.62).
There also appeared to be no association between famciclovir and major birth defects. Results indicated that one infant (3.8%) of the 26 with exposure to the drug had a major birth defect. The researchers noted, however, that use of famciclovir was rare, and therefore, the data should be interpreted with caution.
Analysis also implied no statistically significant relationship between antivirals and major birth defects affecting particular organ systems.
"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 researchers wrote. "Consequently, it has immediate clinical implications and may support informed decisions on safety when prescribing antivirals for herpes infections in early pregnancy."
The researchers also said, however, that future studies should include information on spontaneous abortions, preterm births and breast-feeding.
In an accompanying editorial, James L. Mills, MD, MS, and Tonia C. Carter, PhD, of the NIH, said research on individual defects are lacking, and records on filled prescriptions do not necessarily equate to evidence of medication use. Furthermore, they said birth defects can also appear after the first year of life.
Yet, Mills and Carter said the study still has merit. "At a time when the health care system in the United States is facing enormous financial challenges, it is important not to ignore any sources of data that could answer critical medical questions," they wrote.
For more information:
- Mills JL. JAMA. 2010;859-906.
- Pasternak B. JAMA. 2010;304:859-866.