July 19, 2017

expert reaction to study looking at antibiotics in pregnancy and risk of birth defects

Publishing in the British Journal of Clinical Pharmacology researchers examined links between certain antibiotics during pregnancy and major congenital malformations in newborns.

Prof. Basky Thilaganathan, spokesperson for the Royal College of Obstetricians and Gynaecologists (RCOG), said:

“This is a large scale and well-designed study that shows some antibiotics used during pregnancy are associated with a greater risk of birth defects in newborns, but it is important to note that the absolute risk of a baby developing such a problem is small.

“In addition, the study found only an association, not a causation – therefore, the reason why some babies developed birth defects may not be due to antibiotic use during pregnancy, but other factors that were not measured in the study.  More research will be needed to confirm these findings.

“Antibiotics are only prescribed during pregnancy to treat infections that may potentially harm the mother and baby.  It is important to note that the majority of drugs, including antibiotics, linked to defects are very rarely used in pregnancy nowadays, and any potential risk posed by antibiotic use during pregnancy will probably be far outweighed by the benefits of treatment.

“It is also important to note that doxycycline is a tetracycline and is not used in pregnancy.  The other antibiotics associated with the higher risk (clindamycin, doxycycline, quinolones, macrolides, and phenoxymethylpenicillin) are used more infrequently than the ‘safe’ antibiotics as a second choice when drug resistance, clinical scenario or drug allergies dictate.

“A pregnant woman taking antibiotics should not stop taking prescribed medications based on this latest study.  If she has any concerns about her prescribed medication, she is strongly encouraged to consult her doctor.”

Prof. Stephen Evans, Professor of Pharmacoepidemiology, London School of Hygiene & Tropical Medicine, said:

“I would treat these findings with a great deal of caution.  An extremely large number of possible malformations have been reported in association with a large number of antibiotics.  As the authors say the possibility of false positive findings is very high and their arguments for not applying any multiple comparison corrections (which can help deal statistically with the problems of comparing large numbers of factors and or possible outcomes) are weak.

“More care needs to be taken in studies like this in relation to the timing of drug use and the development of the foetus – in this study we don’t know at what stage of pregnancy these women took antibiotics, so we can’t know how plausible it is that any association is likely to be causal.  I am unconvinced that this has been dealt with properly in my quick read of the study.

“They mention residual confounding and, especially in the case of antibiotics, it is impossible to disentangle the effect of the infection for which the antibiotic is given and the antibiotic itself.

“There are severe dangers in over-interpreting these findings – women should not stop taking antibiotics they have been prescribed.  The infections the antibiotics have been prescribed to treat will likely be more dangerous to the women and their foetuses than the antibiotics themselves.

“The findings of this study could be used to contribute to a proper systematic review of the evidence, though even such a review is subject to the problems of confounding factors.”

* ‘Use of antibiotics during pregnancy and the risk of major congenital malformations: A population based cohort study’ by Flory T. Muanda et al. published in the British Journal of Clinical Pharmacology on Wednesday 19 July 2017.

Declared interests

Prof. Stephen Evans: “No C of I.”

None others received.