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expert reaction to paper looking at cardiac abnormalities in patients with COVID-19 treated with hydroxychloroquine and azithromycin

A paper, published in Nature Medicine, examines cardiac abnormalities in COVID-19 patients treated with the drugs hydroxychloroquine and azithromycin.


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

“This short communication is a study in a single group of patients with Covid-19.  It is not clear whether the diagnosis of Covid-19 was made only on clinical features or following a PCR or other test for SARS Cov-2, but it was a series of 84 consecutive patients with no selection made.

“Both the drugs of interest are known to slightly increase the recovery time for the heart between beats (the QT interval) in healthy volunteers.

“This study used a single group of patients with no comparison group.  While they measured within-patient changes, the absence of a comparator group makes the interpretation less than obvious.

“The changes seen were however quite striking in some patients.  Rises of 10-20 milliseconds are not unusual, but average values above this suggest that there is a problem, certainly for some individuals, and some had rises well over 50ms.  The values of the QT interval were not elevated on average before treatment, but a number had values which went over 500 ms, which is an indicator for a serious heart problem.  It does not seem that these changes resulted in a clinical abnormality of heart rhythm, but there was potential for it.  Because there was no comparison group, it cannot be said with any certainty that the changes were simply due to the drugs, but all the knowledge about those drugs is entirely compatible with these findings.  It seems likely that combining two drugs, each of which can increase the QT interval, is an unwise thing to do unless there is some other clear benefit.

“Measurement of prolongation of the QT interval is complex, and careful studies are usually done in healthy volunteers for new drugs before they reach the market.  The effects on patients who are ill is less well studied generally.  In this study the clinicians were appropriately cautious in carefully monitoring the QT interval in all their patients.”


‘The QT interval in patients with COVID-19 treated with hydroxychloroquine and azithromycin’ by Ehud Chorin et al. was published in Nature Medicine on Friday 24 April 2020.

DOI: 10.1038/s41591-020-0888-2


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