Swiss pharmaceuticals giant Novartis has decided to halt a clinical trial of hydroxychloroquine as a treatment for COVID-19, citing problems in recruiting enough patients for the study of the controversial drug.

"Novartis has made the decision to stop and discontinue its sponsored HCQ clinical trial for COVID-19 due to acute enrolment challenges that have made trial completion infeasible," the company said in a statement late Friday.

This problem "made it unlikely that the clinical team will be able to collect meaningful data in a reasonable timeframe," it said.

"No safety issues have been reported, and there are no conclusions on efficacy from the study."

Hydroxychloroquine and its related compound chloroquine have traditionally been used to treat malaria and with a known anti-viral potential was seen as a possible treatment in the early days of the pandemic.

Despite recognised serious side effects, many prominent figures, including US President Donald Trump, touted it widely as a COVID-19 treatment at a time when there is no vaccine for the disease and other potentially effective drugs are only just beginning to be identified.

In April, Novartis said it would sponsor a Phase III clinical trial of around 440 patients in the US using hydroxychloroquine to treat patients hospitalised with COVID-19 in agreement with the US Food and Drug Administration (FDA).

But earlier this month, the US authorities suspended its use and this week the World Health Organization said it was suspending its trials of hydroxychloroquine because it showed no ability to reduce mortality rates.

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