Recent remarks by US president Donald Trump in a nationally televised White House press conference that the malaria drug chloroquine could be a “game changer” in the fight against the COVID-19 virus continue to make ripples, in one case ending in tragedy.

Beyond malaria, the substance is used to treat other ailments, including lupus, and US press reports say patients who need it are finding it hard to find. Meanwhile, dispensers are having to lock down supply to protect people with compromised immune systems – those most likely to contract the novel coronavirus.

Several US states are now more tightly regulating new prescriptions, with six having issued guidelines allowing existing patients to continue receiving the drugs, while making new prescriptions subject to special approval.

The tighter controls follow reports that some doctors were prescribing the drug “haphazardly” to family and friends to prepare for potential COVID-19 infections.

In the absence of clear clinical results, chloroquine has not yet been approved by the US Food and Drug Administration (FDA) as a treatment, although Bayer – which has donated tablets – said it is working with US health authorities to make it available for testing.

Unregulated sellers have been offering the substance, which outside the human pharmaceutical sector is used in tablets for aquarium cleaning.

Between Feb. 25 and Mar. 2, the price of a single 25-gram bottle of chloroquine phosphate reportedly surged from $9.99 to more than $500. Although online sellers warned that it was not for human consumption, some buyers apparently ignored the advice.

In the western state of Arizona, a man died early this week, and his wife was critical condition, after they inhaled the aquarium cleaning additive. It wasn’t clear whether or not the pair had confirmed COVID-19 infections.

Washington DC newspaper The Hill reported that Nigeria registered two cases of chloroquine poisoning after the US president endorsed it on Twitter.

Although Anthony Fauci, the by now well-known head of the US National Institute of Allergy and Infectious Diseases (NIAID) called evidence that the malaria drug can be useful against COVID “anecdotal,” at least one French health expert has said he believes it may work in some cases.

Didier Raoult, the infectious disease expert who led a partially successful French clinical study with 24 patients, said that despite the small sample size the evidence showed that "hydroxychloroquine treatment is significantly associated with viral load reduction/disappearance in COVID-19 patients, and its effect is reinforced by the antibiotic azithromycin” – a combination Trump praised during his press conference.

French health authorities have allowed the use of chloroquine to treat the coronavirus only in very critical cases in which physicians and health experts agree the risks are manageable.