US President Donald Trump has said he's taking the malaria drug hydroxychloroquine as a preventative measure against Covid-19, although scientists have warned about side effects.
Studies are underway to examine if hydroxychloroquine (and a related drug chloroquine) are effective against the coronavirus.
We've looked at what we know so far about these drugs.
Who's raised concerns about using them?
The World Health Organization has said it's concerned by reports of individuals self-medicating and causing themselves serious harm.
These safety concerns have been echoed by a former top US health official.
Dr Rick Bright, who was removed from his post in April leading the government's vaccine development efforts, says President Trump's focus on these drugs has been "extremely distracting to dozens of federal scientists".
And the US Food and Drugs Administration, which granted emergency approval for using them in certain settings only, has also warned about some possible side effects.
Is there evidence they might treat Covid-19?
President Trump has previously referred to the potential of hydroxychloroquine in White House briefings. At a press conference in April, he said: "What do you have to lose? Take it."
And Brazilian President Jair Bolsonaro claimed in a video that "hydroxychloroquine is working in all places", although that was subsequently removed by Facebook for breaching its misinformation guidelines.
The publicity given to these drugs led to a global surge in demand for them.
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Following Mr Trump's comments in late March, there was a sharp increase reported in prescriptions in the US for both chloroquine and hydroxychloroquine.
Tablets containing chloroquine have long been used in the treatment of malaria to reduce fever and inflammation, and the hope is that they can also work against the virus that causes Covid-19.
There are ongoing trials in various countries on using the drugs to prevent the illness. As part of these studies, frontline workers who are highly exposed to the virus are taking it as a prophylactic.
A trial has begun across Europe, Africa, Asia and South America, testing 40,000 people with either hydroxychloroquine, chloroquine or a placebo to see if it's effective on those who might be exposed to the virus.
Other studies are looking into whether it can help patients who already have Covid-19.
In the US, various trials are under way for a combination of drugs including chloroquine, hydroxychloroquine and an antibiotic called azithromycin, for treating Covid-19 patients.
But so far, there is insufficient evidence from these trials as to their effective use in either prevention or in treatment.
"We need larger, high-quality randomised clinical trials in order to better evaluate their effectiveness," says University of Oxford's Kome Gbinigie, author of a report on anti-malarial testing for Covid-19.
There are also risks of serious side effects, including renal and liver damage.
Which countries authorised their use?
In late March, the US Food and Drugs Administration (FDA) has granted "emergency use" authorisation for these drugs in the treatment of Covid-19 for a limited number of hospitalised cases.
The FDA is not saying they definitely work. But it does mean that in specific circumstances, hospitals can request and use the medicines from government stockpiles for use in Covid-19 treatment.
But on 24 April, the FDA also issued a warning about the dangers of using the substances because of reports of heart rhythm problems in patients.
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