Another study shows that hydroxychloroquine - a drug President Donald Trump said showed promise in treating the coronavirus - appears to not help Covid-19 patients and, instead, places them at increased risk of heart attack.

Hydroxychloroquine taken in conjunction with azithromycin was associated with "significantly elevated levels of cardiac arrest" even after adjusting for factors such as sex, age, underlying health conditions and more severe illness, according to a new study in the JAMA Network published Monday.

The New York State Department of Health, in partnership with the University of Albany, had been conducting a so-called observational study that researchers hoped could shed some insight into the drug's potential effectiveness.

Researchers at the University of Albany's School of Public Health analyzed more than 1,400 medical records of hospitalized patients with Covid-19 across 25 hospitals in the New York metro area between March 15 and March 28.

At least 735 patients received hydroxychloroquine with azithromycin, 271 hydroxychloroquine alone, 211 azithromycin alone, and 221 received neither drug. The researchers said they did not "observe a significant benefit" of the administered drugs.

"This observational study has given us an important early look at some key questions related to prescribing patterns of hydroxychloroquine, azithromycin and chloroquine," David Holtgrave, dean at the University of Albany's School of Public Health and a researcher working with the state, said in a statement to CNBC. "Unfortunately, we did not observe benefits of the most used drug (hydroxychloroquine with or without azithromycin) in this group of seriously ill, hospitalized patients."

Observational studies aren't considered as conclusive as randomized controlled trials, because doctors can prescribe a variety of other drugs to treat an infection. The less formal process, however, can yield faster results and help with the approval process of some treatments.

This is the second study in less than a week to conclude that hydroxychloroquine may not be helpful to patients.

On Thursday, a study published in the New England Journal of Medicine found that the drug didn't appear to help hospitalized patients with Covid-19.

That study, funded by the National Institutes of Health and conducted by researchers at New York-Presbyterian Hospital and Columbia University Irving Medical Center in New York City, looked at 1,376 consecutive patients who showed up at the emergency room with symptoms of coronavirus.

Nearly 60%, or 811 of the patients, received the drug within 48 hours and were found, on average, to be more severely ill than those who didn't receive the drug, the researchers said. They said the study didn't find any potential benefit or harm from the drug, adding a rigorous, randomized clinical trial is needed.

The new findings come after the Food and Drug Administration warned consumers against chloroquine or hydroxychloroquine to treat Covid-19 outside a hospital or formal clinical trial setting.

The agency said it became aware of reports of "serious heart rhythm problems" in patients with the virus who were treated with the malaria drugs, often in combination with antibiotic azithromycin, commonly known as a Z-Pak.

Chloroquine was approved by the FDA in 1949 to treat malaria. Hydroxychloroquine is often used by doctors to treat rheumatoid arthritis and lupus.

The researchers said the findings should be considered by physicians and patients in concert with findings from randomized controlled trials, other empirical studies, NIH treatment guidelines and FDA drug safety communications.

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