The largest retrospective analysis to date of hydroxychloroquine safety shows it is safe for a month, but long-term use — or use with azithromycin — raises the risk of cardiovascular mortality.

An international group of researchers, the OHDSI-COVID-19 consortium*, said they were spurred to embark on the big data study because of concern about the safety of hydroxychloroquine emerging from its use in the pandemic.

Serious adverse cardiac events associated with QT-segment prolongation had occurred in trials of the drug, either alone or with azithromycin, in the US and Brazil, they said.

This had led to “confusion in the rheumatological community regarding the safety implications of hydroxychloroquine within its traditional uses”, they wrote in the Lancet Rheumatology.