An antimalarial drug touted as a potential treatment for coronavirus might have no benefit to patients at all, according to a new study by French scientists.

Researchers compared more than 180 patients – some receiving hydroxychloroquine treatment and others who were not treated with the drug – and found their outcomes were almost identical.

The research by doctors and scientists from 12 hospitals and public research institutes across France, is the most comprehensive study so far of the performance of the controversial drug in hospitals and involves the most Covid-19 patients.

“These results do not support the use of hydroxychloroquine in patients hospitalised for documented Sars-CoV-2-positive hypoxic pneumonia,” the authors said in a non-peer reviewed paper released by medRxiv.org on Tuesday.

Hydroxychloroquine was invented in 1945. It is a chemical compound derived from chloroquine, a drug used by troops to combat malaria in the Pacific jungles during World War II, with similar effect.

Early this year, soon after the first strain of the new coronavirus was isolated, Chinese scientists used a supercomputer to screen for potential drugs. They found chloroquine and its derivatives had a chemical structure that could interact with the virus.

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Preliminary laboratory experiments suggested this family of drugs could suppress viral replication in the test tube, though it remained far from clear what effect it would have on the human body.

US President Donald Trump was the first – and the only – world leader promoting the drug as a hopeful cure for Covid-19 to the general public. The US Food and Drug Administration last month granted an emergency approval that allowed American hospitals to use chloroquine and hydroxychloroquine on Covid-19 patients without clinical trials.

An uncontrolled study by a research team in Marseille, France, involving 26 patients found 100 per cent viral clearance in nose swabs in six patients treated by a combination of hydroxychloroquine and antibiotics, raising hope for the drug.

In a study from Wuhan, China, on 62 patients, researchers also found “significant improvement” on the general outcome. These results, however, were not replicated in follow-up research involving 11 patients in Paris. The conflicting observations have confused the public and health authorities around the world.

So a French team, led by Matthieu Mahevas of the University of Paris-Est, decided to investigate what happened in a “real-world setting”. They pulled the medical records from four hospitals in France of 181 patients of similar gender, age and health conditions. All the patients required oxygen because of lung infections caused by the virus.

The researchers said these patients were more representative of those admitted to hospitals swamped by the pandemic than those in some previous studies. The Wuhan trial, for instance, recruited only patients with mild symptoms, whose chance of recovery was high, even without treatment.

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Among the patients who took hydroxychloroquine upon admission, 20.5 per cent had entered the intensive care unit or had died within a week. Among the patients who did not take the drug, the rate of ICU admission or mortality within a week was 22.1 per cent. The researchers said statistically there was no difference between the two groups.

“In conclusion, we found that hydroxychloroquine did not significantly reduce admission to ICU or death at day seven after hospital admission, or acute respiratory distress syndrome in hospitalised patients with hypoxemic pneumonia due to Covid-19,” the authors said. “These results are of major importance and do not support the use of hydroxychloroquine in patients hospitalised for a documented Sars-CoV-2 pneumonia,” they added.

The doctors’ other concern was side effects. The hydroxychloroquine, although safer than chloroquine, could still cause a wide range of negative effects, including sudden cardiac death.

The French study found nearly 10 per cent of patients taking the drug experienced abnormal heartbeats that required discontinuation of the treatment after about four days. In most of these cases, the heart muscle took longer than normal to recharge between beats.

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“One patient who received no other medication that might interfere with cardiac conduction presented a first-degree atrioventricular block after two days of hydroxychloroquine treatment,” the researchers said.

Research on the chloroquine family of drugs continues around the world as nations try to get the Covid-19 pandemic under control.

Zhong Nanshan, a senior Chinese government scientist in Guangzhou, told local media that his team would soon publish a paper with positive results for chloroquine phosphate, another derivative drug in the chloroquine family.

“The average time [with chloroquine phosphate treatment] for the virus to turn negative is four days, and the control group [without the treatment] is eight or nine days. This improvement of symptoms is very certain,” Zhong told state television on Tuesday. “It can be a very effective cure.”