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In this Commentary on a British study of congenital malformations after use of macrolide antibiotics by pregnant women with data from general practitioners, the importance of high-quality healthcare databases for pharmacovigilance is emphasized. The authors of the British study compared three groups during the study period January 1990 through June 2016: 104,605 children from mothers treated during pregnancy with a macrolide or penicillin, a group of 53,735 siblings, and 82,314 children whose mothers were treated with a macrolide before conception. A significantly increased risk of 55% of congenital malformations was seen for use of macrolides during the first semester in comparison to use of penicillins, especially cardiovascular malformations. Although this well-performed study is the largest up till now, some potential limitations are discussed such as potential exposure and outcome misclassification, as well as confounding by indication.

When drugs are registered, relatively little is known about their adverse effects as clinical trials generally include only small numbers of patients and are of limited duration. New European legislation and the monitoring of adverse events are intended to enable the timely recognition of adverse effects of newly-registered drugs. However, many adverse effects of commonly-used older drugs are already well-known. Therefore, in order to improve the quality of health care, research should also be focused on the risk factors associated with developing such adverse effects.