Macrolide antibiotics possible cause of serious birth defects

Macrolide antibiotics increase the risk of serious birth defects

Children of mothers who were given antibiotics with the macrolide drug class during early pregnancy have an increased risk of serious birth defects, especially heart defects, compared to children of mothers who were prescribed penicillin, as a recent study shows.

Researchers found that macrolide antibiotics, which are particularly often prescribed during pregnancy, are associated with a higher risk of serious birth defects. The research team warns that such antibiotics should be used with caution during pregnancy. The study was recently presented in the renowned British Medical Journal (BMJ).

What are macrolide antibiotics?

Macrolide antibiotics (including erythromycin, clarithromycin and azithromycin) are a relatively new but still widespread class of antibiotics from the macrolide class. They are often prescribed to treat bacterial infections such as bladder or breast infections. Such complaints occur particularly frequently during pregnancy. Macrolide antibiotics are used particularly in people with penicillin allergy.

There were already doubts

In previous studies, there were indications of undesirable side effects with macrolides, which seem to occur particularly in unborn babies. The recommendations for the use of these antibiotics during pregnancy were therefore very different. A research team at University College London has now shed more light on this connection.

Comprehensive analysis

The researchers analyzed the data from two groups: one group comprised 104,605 ​​children born in Great Britain between 1990 and 2016. An average follow-up period of around six years was included in the analysis. The other group included 82,314 children whose mothers were prescribed macrolides or penicillins before pregnancy and 53,735 children who were siblings of children from this group.

What are the risks of macrolide income?

According to the analysis, the prescription of macrolides during the first three months of pregnancy is associated with an increased risk of major malformations and heart defects compared to penicillin. The use of macrolide antibiotics resulted in 28 major birth defects per 1000 cases compared to 18 cases with penicillin intake. In 11 per 1000 cases, heart defects occurred with macrolide intake compared to 7 per 1000 cases with penicillin.

The increased risks disappeared in children of mothers who took macrolides in later pregnancy (after the third month). However, a slightly increased risk of genital malformations was observed throughout the pregnancy. Genital malformations occurred in five per 1000 births, while penicillin in three in 1000 cases.

Cause still unclear

The researchers emphasize that this is an observational study. The cause of this connection is currently unclear. However, the context is consistent and the team believes the results will stand up to further scrutiny. "These results show that macrolides should be used with caution during pregnancy and that alternative antibiotics should be prescribed, if possible, until further research is available," the research team concludes. (vb)

Author and source information

This text corresponds to the requirements of the medical literature, medical guidelines and current studies and has been checked by medical doctors.

Graduate editor (FH) Volker Blasek


  • BMJ: Some antibiotics prescribed during pregnancy linked with birth defects (published: 19.02.2020),
  • Heng Fan, Ruth Gilbert: Finbar O’Callaghan, u.a .: Associations between macrolide antibiotics prescribing during pregnancy and adverse child outcomes in the UK: population based cohort study; in: BMJ, 2020,

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