Antibiotic Associated with Higher Risk of Miscarriage

A new study has found that use of the antibiotic clarithromycin in the first trimester of pregnancy is associated with an increased risk of miscarriage.

Researchers at Copenhagen University Hospital (Denmark) conducted a Danish nationwide cohort study that included all women with a known conception between 1997 and 2007. The researchers identified all women giving birth from the national fertility database, while the national hospital register was used to identify all women with a record of miscarriage or induced abortion; prescription data was obtained from the national prescription register. The primary outcome was the number of miscarriages and offspring with major congenital malformations among users of clarithromycin, compared to nonusers.

In all, the researchers identified 931,504 pregnancies, which resulted in 705,837 live births, 77,553 miscarriages, and 148,114 induced abortions; 401 women redeemed a prescription of clarithromycin in the first trimester, of which 10% experienced a miscarriage. Among the live born, nine women (3.6%) had offspring with malformations. The hazard ratio (HR) of miscarriage after exposure to clarithromycin was 1.56. There was no increased hazard of having a miscarriage when being exposed to penicillin or erythromycin, and there was no increased prevalence of malformations in offspring after exposure to clarithromycin. The study was published on January 2, 2013, in PLOS One.

“We found an increased hazard of miscarriage but no increased prevalence of having offspring with malformations among women redeeming a prescription of clarithromycin in early pregnancy,” concluded lead author Jon Traerup Andersen, MD, and colleagues. “This is supported by previous studies in animals and humans. However, further research is required to explore the possible effect of treatment indication on the associations found.”

Clarithromycin is a macrolide antibiotic used to treat pharyngitis, tonsillitis, acute maxillary sinusitis, acute bacterial exacerbation of chronic bronchitis, pneumonia, and skin and skin structure infections. The drug has been associated with both miscarriage and birth defects in animal studies, and for that reason is not recommended for use by pregnant women. However, since many pregnancies are unplanned and the drug is widely used, a substantial number of women might be at risk, especially during the first trimester.

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