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Antiviral medication exposure safe in first trimester of pregnancy

Clinical Question:
Does antiviral medication use in the first trimester of pregnancy increase the risk of birth defects?

Bottom Line:
Antiviral medications used in the first trimester of pregnancy are not significantly associated with an increased risk of major birth defects. The majority of exposure in this study was to acyclovir (86%) and valacyclovir (13%). Minimal exposure occurred with famciclovir (1%). The authors also found no significant association with exposure to topical antiviral creams. (LOE = 1b)

Pasternak B, Hviid A. Use of acyclovir, valacyclovir, and famciclovir in the first trimester of pregnancy and the risk of birth defects. JAMA 2010;304(8):559-566.  [PMID:20736469]

Study Design:
Cohort (prospective)


Inpatient (any location) with outpatient follow-up

Nearly 1% of women acquire herpes simplex during the first trimester of pregnancy. To determine the safety of antiviral use for these women, the authors analyzed data from a national birth registry, a prescription drug register, and a national patient register in Denmark. Maternal disease and antiviral drug exposure during pregnancy was evaluated controlling for potential confounders, including infectious and sexually transmitted diseases during pregnancy, diabetes, immunodeficiency, drug use for antineoplastic and immunomodulating agents, maternal age at conception, smoking status, and socioeconomic class. Of the total 837,795 live births occurring from January 1, 1996, through September 30, 2008, 2.4% were diagnosed with a major birth defect. Among the 1804 pregnant women exposed to antiviral medications during the first trimester, 2.2% of their infants were diagnosed with a major birth defect. The majority of the exposure was to acyclovir (1561 infants) and valacyclovir (229 infants). Only 26 infants were exposed to famciclovir. A secondary analysis of acyclovir and penciclovir topical creams also found no significant association with exposure and subsequent major birth defects.


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