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Evidence Watch: Carl Heneghan’s selection of evidence that impacts on practice


This week’s Evidence Watch highlights the risk of pre-eclampsia with metformin, the role of repeated influenza vaccination, de-prescribing medications and assessing harms in the elderly at the time of elective surgery.

Carl Heneghan, Editor in Chief

A meta-analysis evaluating the risk of pre-eclampsia in women taking metformin before, or during pregnancy found that there was no difference in risk compared to placebo. [1] But compared to insulin showed a reduced risk. The question remains as to whether metformin is protective or insulin harmful.

Does repeated influenza vaccination prevent severe influenza infection? This case-control study published in the Canadian Medical Association Journal suggests it does. [2] I can’t help thinking there is a lack of randomised trial in this area to inform decision making: using case-control methods to inform policy would be a retrograde step.

A pragmatic cluster RCT in 46 general practices in the Netherlands attempted to deprescribe preventive cardiovascular medications in those where the risks outweighed the potential benefits of treatment. [3] In the intervention group 65% quit their medications, and at 2 years 27% were still not taking them. Predicted CVD risk increased by 2% in the intervention group compared to 1.9% in the usual care group, although BP rose by 6mmHg in the intervention group, suggesting not all folk should have their meds stopped.

Elective surgery can cause significant harm to older adults. This systematic review, in BMC Medicine. highlights the prognostic factors to watch out for at the time of surgery. [4] The review identified 44 studies (12,281 patients) and found that frailty, cognitive impairment, smoking and depression were associated with post-op complications whereas age per se was not.


[1] Risk of pre-eclampsia in women taking metformin: a systematic review and meta-analysis. Alqudah A. et al. 2018. Diabetic Medicine: A Journal of the British Diabetic Association35(2), 160–172.

[2] Repeated influenza vaccination for preventing severe and fatal influenza infection in older adults: A multicentre case-control study. Casado I. et al.  CMAJ. 2018 Jan 8;190(1):E3-E12. doi: 10.1503/cmaj.170910

[3] Deprescribing preventive cardiovascular medication in patients with predicted low cardiovascular disease risk in general practice – the ECSTATIC study: A cluster randomised non-inferiority trial. Luymes C.H. et al. 2018. BMC Medicine16(1), 5.

[4] Identifying older adults at risk of harm following elective surgery: A systematic review and meta-analysis. Watt J. et al. 2018. BMC Medicine16(1), 2.

BMJ Evidence-Based Medicine – original evidence-based research, insights and opinions on what matters for health care.

BMJ EBM accepts submissions of a wide range of article types, including original research, debate, analysis & opinion, and clinical spotlight.

We select from over 100 journals reliable and useful evidence summarised in BMJ Evidence-Based Medicine.

Read more about BMJ EBM content in the Welcome to BMJ Evidence-Based Medicine Editorial.



Carl Heneghan is Professor of EBM at the University of Oxford, Director of CEBM and Editor in Chief of BMJ EBM

Follow on twitter @carlheneghan

Competing interests

Carl has received expenses and fees for his media work including BBC Inside Health. He holds grant funding from the NIHR, the NIHR School of Primary Care Research, The Wellcome Trust and the WHO. He has also received income from the publication of a series of toolkit books published by Blackwells. CEBM jointly runs the EvidenceLive Conference with the BMJ and the Overdiagnosis Conference with some international partners which are based on a  non-profit model. 

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