Hydroxychloroquine ineffective as post-exposure prophylaxis for COVID-19: study

According to study findings published Wednesday in the NEJM, hydroxychloroquine did not prevent COVID-19 in people who had been exposed to patients infected with the virus. "The take-home message for the general public is that if you're exposed to someone with COVID-19, hydroxychloroquine is not an effective post-exposure, preventive therapy," commented lead author David Boulware.

The study is the first controlled clinical trial testing whether the antimalarial drug could prevent illness in people who have been exposed to SARS-CoV-2, although it did not address whether it can prevent infection if people take it before they are exposed. The study involved 821 people, recruited online, across the US and Canada who had either high- or moderate-risk exposure to a person who had tested positive and was ill with COVID-19.

Most at 'high-risk' exposure

High-risk exposure meant people were less than six feet from a patient for more than ten minutes, wearing neither a mask nor a face shield, with about 88% of study participants falling this group. Moderate risk meant they wore a mask, but no face shield. Meanwhile, none of the subjects exhibited any symptoms of COVID-19 themselves. Study participants ranged in age from 33 to 50 years, with a median age of 40, they were split roughly evenly between men and women, and were considered to be healthy. In addition, 66% of the total consisted of healthcare workers, with most of the remaining having been exposed at home, to an infected spouse, partner or parent.

Within four days of exposure, subjects were randomly assigned either hydroxychloroquine or placebo, and then followed to determine whether they had either laboratory-confirmed COVID-19 or an illness consistent with the virus, during the next 14 days. However, the authors acknowledged that due to a shortage of test kits in the US, the "vast majority" of participants, including healthcare workers, were unable to access testing, "thus, an a priori symptomatic case definition was used."

No serious safety issues

Results showed that 11.8% of patients in the hydroxychloroquine arm became ill, versus 14.3% for placebo, a difference that was not statistically significant. Hydroxychloroquine also did not appear to make the illness any less severe. Meanwhile, adverse events, such as nausea or diarrhoea, were more common in hydroxychloroquine-treated subjects than in the placebo group, occurring at rates of 40.1% and 16.8%, respectively, but there were no problems with heart rhythm or any other serious adverse effects reported.

The authors noted there were limitations in the study, including that trial methods did not allow consistent proof of exposure to SARS-CoV-2 or consistent laboratory confirmation of SARS-CoV-2 infection. "Indeed, the specificity of participant-reported COVID-19 symptoms is low, so it is hard to be certain how many participants in the trial actually had COVID-19," noted an accompanying editorial published in NEJM.

Pre-exposure prophylaxis?

Still, based on the results, Boulware recommended against using hydroxychloroquine to protect people who have already been exposed to the virus. However, whether the drug may still work as pre-exposure prophylaxis in high-risk populations is "a separate question, with trials ongoing," the authors said.

The latest news comes in the wake of disappointing results from a pair of studies published in the BMJ indicating that hydroxychloroquine did not significantly help patients with COVID-19. Meanwhile, a recent study published in The Lancet that had linked hydroxychloroquine and chloroquine to increased risk of irregular heart rhythms and death among COVID-19 patients, and which also led to the World Health Organization (WHO) suspending the hydroxychloroquine arm of its global Solidarity Trial, has since been called into question. On Wednesday, the WHO resumed its study of the drug following a safety review. 

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