October 2, 2013
Little Evidence That Antihistamines Raise Birth Defect Risks

Boston—Antihistamines, whether prescription or OTC, do not appear to increase birth defects in unborn children when taken by pregnant women.

A new study from Boston University’s Slone Epidemiology Center is based on interviews with more than 20,000 new mothers about antihistamine usage, and it found little evidence that any specific drug might be linked to an increased risk of a specific birth defect. The study, which appears in the Journal of Allergy and Clinical Immunology: In Practice, notes that, while a few associations require greater research attention, the findings could be due to chance.

For the study, researchers used 1998-2010 data from the Slone Epidemiology Center Birth Defects Study, a multicenter, case-control surveillance program of birth defects in North America, to test 16 previously hypothesized associations between specific antihistamines and specific birth defects, as well as to identify possible new associations.

Mothers were interviewed within 6 months of delivery about demographic, reproductive, medical, and behavioral factors, and details on the use of prescription and nonprescription medications. First trimester exposure to specific antihistamines was compared between 13,213 infants with specific malformations and 6,982 nonmalformed controls.

Antihistamines included in the study all had previously been suggested to increase risks of certain defects. The researchers also considered other possible risks that might not have been identified in the past.

During the first trimester, 13.7% of controls were exposed to antihistamines, according to the report, with the most commonly used medications being diphenhydramine (4.2%), loratadine (3.1%), doxylamine (1.9%), and chlorpheniramine (1.7%).

In situations where there was sufficient information in the study data, the authors found no evidence to support suggestions of risk that had been found in earlier studies.

“When estimates were stable, none supported the previously hypothesized associations. Among more than 100 exploratory comparisons of other specific antihistamine-defect pairs, 14 had odds ratios ≥1.5, of which 6 had 95% CI bounds excluding 1.0 before but not after adjustment for multiple comparisons,” the authors write.

“While our findings provide reassurance about the relative safety of many of these medications in relation to a number of common birth defects, more information is needed,” said Allen Mitchell, MD, the study’s director. “As is the case for all types of medications, women who are pregnant or may become pregnant should consult with their health care provider before taking any medicines, whether they are prescribed or OTC.”

Mitchell also noted that the study considered “commonly-used antihistamines that were available OTC as well as those available only with a prescription.”

“Our findings do not provide meaningful support for previously posited associations between antihistamines and major congenital anomalies; at the same time, we identified associations that had not been previously suggested,” according to study authors. “We suspect that previous associations may be chance findings in the context of multiple comparisons, a situation that may also apply to our new findings.”

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