Robin Ferner

Months or years, I think, rather than a definite answer within weeks, I'm sad to say.

Well, there are two different uses for chloroquine or hydroxychloroquine.

In India, the government has proposed that those who are at high risk of getting COVID-19, for example, healthcare workers, might take chloroquine once a week.

in the hope of preventing the virus from taking hold.

Well, that's very similar to the dosing that's used to prevent malaria or was used to prevent malaria.

And the risks of that are quite well known.

At the other extreme, we know that very large overdoses of chloroquine are extremely toxic.

So when patients take 20 tablets, many unfortunately die.

In between, there is the acute treatment that's been suggested, particularly in France,

for COVID-19, which involves the administration of 6 grams of chloroquine over 10 days, and that's a fair amount, and it's likely to cause much more in the way of adverse effects than the rather small once-weekly dose that's taken to try to prevent the infection.

So the most common adverse effect of chloroquine and of hydroxychloroquine is gastrointestinal upset, diarrhea and vomiting, if you like, or at any rate, nausea.

But on top of that, from time to time, there are cases of bone marrow failure.

Higher doses cause people to become disoriented and even psychotic.

And a particular worry in this context is that in combination with other drugs, chloroquine and hydroxychloroquine can alter the way in which the heart rhythm works.

and produce what, in technical terms, is called QT prolongation.

I looked at the historical context, so people had high hopes for chloroquine or hydroxychloroquine in a whole series of virus infections.

By way of example, there was a large trial to see whether it prevented influenza in over 1,500 people, and there's no evidence that it does.

It seems to have slight effects in HIV, but of course there are much better drugs.

And in some infections, it almost certainly makes things worse.

So the historical perspective doesn't make me optimistic, as there are drugs that interfere with the replication of viruses that depend on RNA, like SARS-CoV-2.