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U.S. President Trump, seen here in Washington on April 8, 2020, is proposing that the drug be used not only as a treatment, but as a way of preventing infection, for COVID-19.Chip Somodevilla/Getty Images

U.S. President Donald Trump has been touting the drug hydroxychloroquine with all the subtlety of a carnival barker.

From his White House bully pulpit, he has, among other things, called it “the biggest game-changer in the history of medicine.”

Given his propensity for bluster, it would be easy enough to laugh that off. But many people take Mr. Trump’s statements as gospel, so there’s a run on the drug and cries to prescribe it widely.

So what is hydroxychloroquine?

The drug, sold under the brand name Plaquenil and in generic form, has two principal uses: as an antimalarial (taken by travellers to prevent infection) and as a treatment for rheumatic diseases such as lupus.

It is also being used, in some instances, to treat patients with COVID-19.

What Mr. Trump is proposing, however, is that the drug be used not only as a treatment, but as a prophylaxis, a way of preventing infection.

“I may take it, okay? I may take it,” he said on Saturday. “I’ll have to ask my doctors about that, but I may take it.”

Hopefully his doctors will tell him truthfully that there is precisely zero evidence that hydroxychloroquine can prevent coronavirus infection. The drug can prevent malaria, but not COVID-19.

The treatment part of the equation looks slightly more promising but, again, there is no evidence at all to back the grandiose claims of Mr. Trump and other hucksters.

The principal argument the President has used in support of hydroxychloroquine is the rhetorical statement: “What do we have to lose?” (He repeated that phrase five times at his Saturday media briefing.) “I’m not a doctor but I have common sense,” Mr. Trump added.

“Common sense” is not evidence. And “what have we got to lose?” is certainly no way to practise medicine – or policy-making for that matter.

Physicians in China started using hydroxychloroquine to treat COVID-19 patients early in the pandemic. There was certainly some logic to this move. The drug has antiviral properties and showed some promise in vitro but that doesn’t mean it will work in vivo.

It remains a desperation drug, something to try when the rest of the very limited armamentarium has been exhausted.

The evidence of benefit in patients is mostly anecdotal, based on highly publicized but scientifically weak studies. Controversial microbiologist Didier Raoult has made wild claims about the effectiveness of hydroxychloroquine but his study, published in the International Journal of Antimicrobial Agents, is little more than anecdotal.

Similarly, Vladimir Zelenko, a small-town doctor in New York State, has gained internet fame promoting a cocktail of three drugs – hydroxychloroquine, the antibiotic azithromycin and zinc sulphate. There is no real evidence for claims that he has cured hundreds of cases of COVID-19, but that hasn’t stopped Mr. Trump from promoting the regimen.

There needs to be proper studies done, with control groups – meaning one group gets the drug(s) and the other does not, and the outcomes are compared. Like it or not, that takes time.

Impatience is not an excuse to make unsubstantiated claims.

Neither is greed. And there are reports that Mr. Trump and his cronies have stakes in Sanofi, the maker of Plaquenil, and related companies, and stand to profit handsomely from his whipped-up frenzy for the drug.

Despite the President’s claim, there is also a lot to lose for patients. Every drug that has effects has side effects.

While hydroxychloroquine is a relatively safe drug, it can cause significant adverse events, including heart arrhythmia (irregular heartbeat) and hypoglycemia (low blood sugar), both of which can be fatal; it can also have neuropsychiatric effects such as agitation, confusion, hallucinations and paranoia.

Just as importantly, patients who need these drugs for continuing treatment of conditions such as lupus are seeing supplies sapped and their lives put at risk by speculators and hoarders.

In the end, hydroxychloroquine may prove helpful to COVID-19. In fact, let’s hope so, because there is little else, other than another experimental approach, using antibodies-rich plasma transfusions. But demonstrating effectiveness (or ineffectiveness) is going to take some time.

Good science is always worth waiting for.

In the meantime, the notion of prescribing hydroxychloroquine to the general public on a prophylactic basis is not a no-lose proposition, it’s sheer madness.

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