France's drug safety agency warned on Monday of potentially serious side effects of treatments being tested against the new coronavirus after the deaths of three people possibly linked to self-medication.

Another two dozen patients have reported undesirable side effects after taking Plaquenil -- the brand name of hydroxychloroquine -- as well as other medicines such as the antiretroviral Kaletra, the agency's head Dominique Martin told AFP.

He said experts were trying to determine whether the drugs were linked to the side effects, with initial conclusions expected by the end of the week. The drug safety agency (ANSM) began boosting its surveillance two weeks ago of trials of drugs against COVID-19, "in particular when they are used outside of clinical trials of chloroquine, hydroxychloroquine, azithromycin, lopinavir/ritonavir (Kaletra), tocilizumab (and) colchicine," Martin said.

"It's perfectly normal that treatments be tried, given the circumstances, but that doesn't mean we shouldn't observe surveillance... of these substances," Martin said.

Combining hydroxychloroquine with the antibiotic azithromycin has been in the spotlight since French researcher Didier Raoult published two studies that he said showed the treatment's effectiveness against COVID-19.

The treatment needs "particular attention", Martin said, because using the two drugs together runs the risk of arrhythmia and could provoke a heart attack. This was "even more the case with patients suffering from COVID-19" because of metabolic problems associated with the disease, he said.

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