A slew of new studies are raising fresh doubts on whether malaria pills should be used to treat the coronavirus, and a top US health agency just warned against widespread use

• A new clinical study in Brazil raises safety concerns about coronavirus patients taking a high dose of the anti-malaria drug chloroquine.
• The trial is one of several recent reports that suggest caution in widely using chloroquine or hydroxychloroquine in people infected with the novel coronavirus.
• The recent studies have limitations that prevent definitive conclusions from being reached about the drugs.
• In the meantime, leading US health agencies have cautioned against treating COVID-19 patients with these drugs.
• There is no high-quality evidence showing these medicines help COVID-19 patients. Large studies that can answer that question are now underway.
• Visit Business Insider's homepage for more stories.

A clinical trial in Brazil testing a high dose of chloroquine to treat hospitalized COVID-19 patients was halted after a spike in deaths among patients who got the drug.

The Brazilian trial, published on Friday in an American Medical Association journal, adds to a pile of confusing evidence around using the anti-malaria pills called chloroquine and hydroxychloroquine for coronavirus patients.

There's no high-quality evidence showing the medicines help patients with COVID-19, the disease caused by the coronavirus pandemic. The US Food and Drug Administration warned Friday these drugs should only be used in clinical trials or in a hospital, due to safety risks to patients. The National Institutes of Health has advised caution in prescribing them.

New York Gov. Andrew Cuomo said Thursday night that a review of medical records by State University of New York at Albany researchers found that the drug "didn't really have much of an effect on the recovery rate."

That conclusion comes from a preliminary look at an observational study of about 600 people. Data from the study hasn't been published or reviewed by outside scientists, and Cuomo revealed the information in a CNN town hall broadcast. Cuomo's office and a researcher working on the study didn't immediately respond to requests for comment.

Trump has touted the malaria drugs to treat the coronavirus

President Donald Trump has touted the malaria drugs by name at his daily press conferences, saying they could be game-changers in the fight against the coronavirus. Demand has surged, making it difficult to find the medicine for some arthritis and lupus patients who depend on the pills.

The idea of using hydroxychloroquine as a COVID-19 treatment took a hit earlier thanks to a study of patients with a severe form of the disease. That review of 368 people found no difference in ventilation risk between those receiving hydroxychloroquine alone, in combination with the antibiotic azithromycin, or just supportive care. That study has yet to be peer-reviewed or published in a medical journal.

Like other chloroquine and hydroxychloroquine research that's been made available so far, the Brazilian study is filled with limitations that prevent strong conclusions from being reached. The findings were published Friday in the Journal of the American Medical Association Network Open.

Read more: Why experts are skeptical of studies that seemed to show promising results from using a decades-old malaria drug to treat the coronavirus

The study was supposed to enroll 440 people hospitalized with severe disease from COVID-19. Participants randomly received either a low or high dose of chloroquine for 10 days. These early findings are based on the first 81 patients enrolled, as researchers requested an early look at the data to check for safety problems.

An alarming warning from a clinical trial

They found an alarming signal: a spike of deaths in the high-dose arm. These patients were receiving 1,200 milligrams of chloroquine per day, well above the range being tested in many other studies. The low-dose group received an initial dose of 900 milligrams on the first day followed by 450 milligrams daily.

While patients were randomly assigned to the two groups, those in the high-dose group were seven years older on average and had more heart problems.

The primary safety concern with these anti-malaria drugs is that they can prolong how long the heart relaxes between beats, which can lead to life-threatening side effects.

Every patient in the study was also taking the antibiotic azithromycin, and nearly 9 in 10 were also taking oseltamivir, an antiviral drug used for the flu also known as Tamiflu.

Both of those drugs also carry the risk of lengthening how long the heart relaxes between beats. Taking all three simultaneously likely amplifies that risk, particularly for patients that are already very sick or elderly.

Read more: We just got more promising data on Gilead's potential coronavirus drug. Here's everything we know about remdesivir and 14 other leading coronavirus treatments.

Better studies are underway

Overall, 39% of the high-dose group died compared to 15% of the low-dose cohort. The small sample size, group imbalances by age and health, and the simultaneous use of several other experimental drugs limits the ability to directly connect chloroquine use with the deaths.

"The preliminary findings of this study suggest that the higher [chloroquine] dosage should not be recommended for critically ill patients with COVID-19 because of its potential safety hazards, especially when taken concurrently with azithromycin and oseltamivir," the Brazilian researchers concluded.

There are several high-quality studies that are designed to randomly assign patients to get.either the malaria drugs or a placebo, and where both the doctors and patients are blinded to knowing which one they are using. These trials are being run by the Swiss pharma giant Novartis, the University of Oxford, and the Bill and Melinda Gates Foundation.

Read more: The US is sprinting to develop a coronavirus vaccine or treatment. Here's how 19 top drugmakers are racing to tackle the pandemic.

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