Clarithromycin may increase miscarriage risk

The use of clarithromycin in the first trimester of pregnancy may increase the risk of miscarriage, according to researchers in Denmark. However, the researchers did not find a link between exposure to clarithromycin and major congenital malformations.

“This study demonstrates that treatment with clarithromycin in the first trimester of pregnancy was associated with a 50% increase (hazard ratio) of miscarriage compared to no treatment and a similarly increased risk compared to penicillin and erythromycin,” wrote Jon Trærup Andersen of the Department of Clinical Pharmacology at Bispebjerg Hospital in Copenhagen, Denmark, and colleagues. Results of the study were published online in the journal Plos One.

The researchers noted that the use of clarithromycin has been associated with miscarriage and birth defects in animal studies. Since many pregnancies are unplanned and treatment with the antibiotic is common, they wrote, “a substantial number of women” risk exposure in early pregnancy. The researchers’ aim was to quantify this risk.

The authors used Denmark’s Fertility Database to identify 931,504 women who gave birth between 1997 and 2007. The researchers also pulled data from the National Hospital Register to identify all women with a record of miscarriage or induced abortion. The authors then obtained prescription data from the National Prescription Register.

The authors noted 705,837 live births, 77,553 miscarriages, and 148,114 induced abortions. Of 401 women who filled a prescription for clarithromycin in the first trimester, 40 (10.0%) experienced a miscarriage compared with 77,513 (8.3%) women who were not exposed to clarithromycin. Nine (3.6%) children born to women exposed to clarithromycin were diagnosed with malformations compared with 24,808 (3.5%) children born to unexposed women. The data did not show an increased risk of miscarriage for women who were exposed to penicillin or erythromycin.

“Although this is a small study with limited power, the result is supported by three other studies,” the authors wrote. However, they caution that further research is required to explore the possible effect of treatment indication on the associations found.