Macrolide antibiotics (azithromycin, clarithromycin, erythromycin, spiramycin, telithromycin etc.) carry a higher risk for major foetal malformations than penicillins when taken during pregnancy, according to a study in the BMJ. This is consistent with prior studies.
Using the U.K.'s national primary care database, researchers compared outcomes in 100,000 children whose mothers, during their gestation, were prescribed a single course of monotherapy with either a macrolide or a penicillin.
In the macrolide group, the prevalence of major malformations (principally cardiovascular) associated with first-trimester prescriptions was roughly 28 per 1000 live births, versus 18 with penicillins. Second- and third-trimester macrolide prescriptions showed no increased risk. Macrolide prescriptions in any trimester were associated with increased genital malformations, mainly hypospadias, at rates of roughly 5 versus 3 per 1,000 births. The authors estimate an additional 4.1 children per 1,000 births would have cardiovascular malformations resulting from the use of macrolides versus penicillins in the first trimester, and they "recommend use of alternative antibiotics when feasible."