Are Macrolide Antibiotics Safe During the First Trimester?

Antibiotics are often administered during pregnancy, and disentangling their effects from those of infection on the fetus is difficult. To clarify the effects of macrolide antibiotics administered during gestational weeks 4 to 13 (when organogenesis occurs), investigators queried a large U.K. database including 100,000 pregnancies between 1990 and 2016. Women who received macrolides (erythromycin, azithromycin, or clarithromycin) were compared with those who received a penicillin antibiotic.

Among children whose mothers received first-trimester macrolides, incidence of major malformations was higher than among those whose mothers who received a penicillin antibiotic (28 vs. 18 per 1000 person-years; adjusted risk ratio, 1.5). Specifically, r…