A clinical trial of anti-malarial drugs involving Oxford healthcare workers has been paused following guidance from the Medicines and Healthcare products Regulatory Agency (MHRA) warning of safety concerns surrounding hydroxychloroquine.

A paper encompassing results from more than 96,000 patients and published in the Lancet medical journal has found that people taking the drug were at a higher risk of death and heart problems. The release of the paper has led the World Health Organisation to remove hydroxychloroquine from its global study into experimental coronavirus treatments “while the safety data is reviewed by the data safety monitoring board,” according to WHO director-general Tedros Adhanom Ghebreyesus. 

The trial, called COPCOV, had initially sought to test whether chloroquine and hydroxychloroquine could prevent healthcare workers exposed to Covid-19 from contracting the virus. More than 40,000 people globally were set to participate in a randomised clinical trial, including NHS staff at the John Radcliffe Hospital in Headington.

A statement released on the trial’s website yesterday said: “We responded promptly to the MHRA, addressing their concerns in detail and await their decision. The safety of our participants is our first priority, as is preventing illness in front-line healthcare workers.”

The study had been given added urgency amidst conflicting reports on the efficacy and safety of hydroxychloroquine. A note accompanying the trial’s original announcement noted that “despite the lack of strong evidence” chloroquine and hydroxychloroquine continue to be widely recommended globally, and so conducting a clinical trial “is of tremendous importance”.

Professor Sir Nicholas White, a Supernumerary Fellow in Tropical Medicine at St John’s College who is one of the principal investigators of the COPCOV study, said at the beginning of the trial: “We really do not know if chloroquine or hydroxychloroquine are beneficial or harmful against Covid-19.” 

“The best way to find out if they are effective in preventing Covid-19 is in a randomised clinical trial” – a trial in which neither participants nor researchers know who has been given which drug.

Hydroxychloroquine has gained international attention as a possible treatment for coronavirus after US President Donald Trump told reporters he was taking it as a preventative measure, despite there being no proven link between the drug and preventing Covid-19 transmission. 

The drug works by regulating the body’s immune system and has been used to treat rheumatoid arthritis and Lupus, as well as malaria, although it is also known to cause dangerous heart arrhythmias.

However, the University of Oxford-based RECOVERY trial remains open and is continuing to trial hydroxychloroquine, amongst other possible treatments, in 10,000 UK patients already admitted to hospital with COVID-19. 

In a statement, the Chief Investigators of the trial said: “We have been working over the weekend to understand the implications of the Mehra [the lead author of the paper released in the Lancet] paper for the safety and welfare of patients randomised to hydroxychloroquine.”

An independent and urgent review of the data that the trial has so far collected “found that the effects of hydroxychloroquine on mortality reported in the analysis by Mehra were not consistent with those observed in the RECOVERY trial.”

The trial will therefore continue uninterrupted, and randomised patients will continue to receive the drug.