The Food and Drug Administration said on Monday that it was revoking emergency authorization of two malaria drugs to treat Covid-19 in hospitalized patients, saying that they are “unlikely to be effective” and could carry potential risks.
The drugs, hydroxychloroquine and chloroquine, were heavily promoted by President Trump after a handful of small, poorly controlled studies suggested that they could work against the disease caused by the coronavirus. Mr. Trump said he took hydroxychloroquine after he had been exposed to two people who tested positive for the coronavirus.
The agency said that after reviewing some data, it determined that the drugs, particularly hydroxychloroquine, did not demonstrate potential benefits that outweighed their risks. Earlier this spring, the F.D.A. had also issued a warning that the drugs could cause dangerous heart arrhythmias in Covid-19 patients.
The review that led to the revocation found more than 100 cases of serious heart disorders in Covid-19 patients taking the drugs, including 25 that were fatal. Other problems were linked to the drugs as well.
Lawmakers and some public health experts have criticized the Trump administration for politicizing the government’s medical and science arms during the pandemic, and of pressuring agencies like the F.D.A. to relax its standards for drugs and medical devices, to get them on the market faster.
“The F.D.A. withdrew an emergency use authorization that never should have been issued in the first place,” Senator Ron Wyden, Democrat of Oregon, said in a statement. “By ignoring science and caving to political pressure from the White House, the F.D.A. stoked false hope and put American lives in danger, while damaging the agency’s reputation in the process.”
On Monday, Mr. Trump stood by his support of the drugs, saying at a White House round table, “All I know is that we’ve had some tremendous reports.” He added: “It certainly didn’t hurt me. I feel good.”
Dr. Peter Lurie, the president of the Center for Science in the Public Interest, said the F.D.A.’s move showed “how, in the end, science can triumph over celebrity and unscientific pronouncements from the White House. In the end, the truth comes out.”
Dr. Lurie said that while some clinical trials of hydroxychloroquine were still underway, so far the evidence “keeps going in the same direction” — that the drug is not effective to treat Covid-19.
In March, the F.D.A. authorized hospitals to use stockpiles of the drugs, which pharmaceutical companies had donated, to treat patients with the virus. Doctors have always been able to prescribe the drugs to individual patients as they see fit.
But in a letter on Monday revoking the authorization, the agency said that further studies had shown that the two drugs were unlikely to be effective in stopping the virus, and that national treatment guidelines didn’t recommend using them outside of clinical trials.
According to the letter, written by Denise M. Hinton, the F.D.A.’s chief scientist, the request to revoke the authorization came from the Biomedical Advanced Research and Development Authority, the unit of the Department of Health and Human Services that had initially asked for the authorization.
In April, the head of that unit, Dr. Rick Bright, said he was removed from his post after he pushed for rigorous vetting of hydroxychloroquine, even as Mr. Trump and his allies were enthusiastically promoting it.
The use of hydroxychloroquine spiked after Mr. Trump continuously praised its potential, calling it a possible “game changer” and saying, “What the hell do you have to lose?” His repeated promotions during daily briefings at the White House prompted runs on pharmacies, threatening supplies for the drugs, which are also taken by people with rheumatoid arthritis and lupus.
Alex M. Azar II, the secretary of health and human services, said at the round table Monday that the F.D.A.’s action only ended the authorization for hospitals to use federal stockpiles of the drugs on hospitalized patients and noted that doctors could still prescribe the drugs to patients.
“In fact the F.D.A. removal of the emergency use authorization takes away what had been a significant misunderstanding by many that had made people think it could only be used in a hospital setting,” he said.
Interest in hydroxychloroquine has waned in recent weeks as further studies showed that the drug did not appear to be effective in treating or preventing Covid-19. Earlier this month, a study of 821 people who had been exposed to patients infected with the virus showed that the drug did not prevent infection.
In May, an article in The Lancet about another study concluded that hydroxychloroquine and chloroquine did not help patients and might have harmed them — but that study was later retracted after the authors could not verify the database of medical records on which the article was based.
As of May 6, there were 347 adverse events in Covid-19 patients taking hydroxychloroquine, and 38 in those taking chloroquine (which is used less often), the F.D.A. said, based on a search of its own database and reports to poison-control centers. The majority of cases, 69 percent, involved men with a median age in the early 60s.
The total included 109 serious heart problems, including 80 cases of a serious heart rhythm disorder called QT prolongation. Other patients had different rhythm abnormalities. Over all, 25 of the 109 died. Many who had cardiac effects had been given other drugs at the same time, like the antibiotic azithromycin, that can also cause QT prolongation.
There were also serious adverse events not affecting the heart in 113 cases, including liver abnormalities, which are listed on the drugs’ labeling as a possible problem. Some patients had severe kidney problems, but renal disease has been linked to the coronavirus itself.
Four patients developed a blood disorder called methemoglobinemia, and two died. That condition is not mentioned in the drugs’ labeling, but had been known as a rare side effect of some medications.
It was not possible to calculate rates of the adverse events, because the total number of patients given the drugs was not known, the F.D.A. said.
The agency also issued a warning Monday about combining hydroxychloroquine or chloroquine with remdesivir, a recently authorized treatment for patients with Covid-19. The F.DA. said the malaria drugs could interfere with remdesivir’s ability to fight the virus.
Several trials of hydroxychloroquine are still underway, including additional studies of whether it can be used to prevent coronavirus infection. The World Health Organization resumed a study of the drug after briefly halting it in the wake of the Lancet article.
Two arms of the National Institutes of Health — the National Heart, Lung and Blood Institute and the National Institute for Allergy and Infectious Diseases — are conducting clinical trials of hydroxychloroquine. Dr. Francis Collins, the N.I.H. director, said those studies would continue.
“I think that would be unfortunate not to,” Dr. Collins said. “What’s been missing here are really well-designed, randomized placebo-controlled trials for hospitalized patients.”
Hydroxychloroquine is still being embraced elsewhere, including in Brazil, which is battling an explosive outbreak.
Members of Congress have questioned increases in the F.D.A.’s granting of emergency use authorizations during the pandemic for certain drugs as potential treatments. They have also questioned authorizations for antibody and diagnostic tests whose data had not been thoroughly vetted before approval, and for certain types of masks and other devices.
Some Democratic lawmakers have criticized the Trump administration for pressuring the agency into issuing too many emergency approvals.
In some cases, the F.D.A. has recently rescinded emergency approvals for use or reuse of some masks and told companies that did not meet a deadline for submitting data on antibody tests that they should not be selling them. The Government Accountability Office recently testified that it planned to look into the F.D.A.’s emergency authorizations.
On Monday, Democrats framed the news as further evidence that Mr. Trump cannot be relied upon in the coronavirus pandemic. Senator Chuck Schumer, the minority leader from New York, said on Twitter, “On medical issues like on so much else, he doesn’t know what he is talking about.”
Denise Grady, Sheryl Gay Stolberg and Michael Crowley contributed reporting.