The National Institutes of Health (NIH) in the US has suspended a clinical trial being performed to assess the safety and effectiveness of hydroxychloroquine to treat adults with Covid-19.

This decision comes after a data and safety monitoring board (DSMB) found that the drug is not likely to be beneficial in this indication compared to placebo. NIH noted that the data indicated no harm with the drug.

After a fourth interim analysis, the DSMB recommended the National Heart, Lung, and Blood Institute (NHLBI) to halt the study.

The blinded, placebo-controlled randomised trial was designed to enrol more than 500 Covid-19 patients, with around 470 recruited at the time of the trial’s closure.

Participants were given hydroxychloroquine 400mg twice daily for two doses, followed by 200mg twice daily for the next eight doses, or a placebo twice daily for five days.

NIH said in a statement: “The data from this study indicate that this drug provided no additional benefit compared to placebo control for the treatment of Covid-19 in hospitalised patients.”

Meanwhile, Swiss pharmaceutical company Novartis has also decided to suspend its hydroxychloroquine trial for Covid-19 over enrolment challenges, which made completion of the trial infeasible.

The company also noted that no safety issues have been reported and no conclusions have been made on efficacy from its trial.

A statement from Novartis read: “The recruitment challenge facing our HCQ trial has made it unlikely that the clinical team will be able to collect meaningful data in a reasonable timeframe to determine the effectiveness of HCQ in treating patients with Covid-19.”

The company will continue to supply the drug for certain ongoing investigator-initiated trials (IITs) and upon government requests.

Earlier this month, the UK’s Medicines and Healthcare products Regulatory Agency (MHRA) suspended enrolment of participants for all Covid-19 clinical trials of hydroxychloroquine across the country.