By Michael Erman and Saumya Joseph

(Reuters) – Results of a study of Regeneron Pharmaceuticals Inc and Sanofi SA’s rheumatoid arthritis drug Kevzara indicate it may only help the sickest coronavirus patients, the companies said on Monday, dampening hopes the medicine could benefit a wider group of those infected.

The drugmakers said they would continue to test high doses of Kevzara only in those who are considered critically ill with COVID-19, the disease caused by the highly contagious virus. The decision was based on guidance from an independent committee that reviewed early trial data, which showed it did not help patients deemed severely ill.

Patients who required mechanical ventilation or high-flow oxygen therapy or treatment in an intensive care unit were considered critically ill. Those who required oxygen without mechanical or high-flow oxygenation were considered severely ill.

There are currently no approved treatments specifically for the novel coronavirus, so drugmakers are rushing to test existing medicines as well as experimental therapies in the hope that something will help alter the course of the illness that has infected more than 3 million people and killed over 208,000 worldwide.

Regeneron co-founder and Chief Scientific Officer George Yancopoulos said he was skeptical about the prospect of drugs like Kevzara that were not designed to treat COVID-19. Drugs currently in late stage testing for the virus, like Gilead Science’s remdesivir, were developed for other diseases.

“Repurposing a drug and finding it to be very effective for a new indication is an exception, as opposed to the rule,” Yancopoulos said. “It’s very, very rare where those have really turned into important drugs for whole new indication.

“It’s hard enough to design a drug and get it to work,” he added.

Regeneron has identified hundreds of virus-neutralizing antibodies and is working to select the best two candidates for a “cocktail” therapy that might treat and even prevent COVID-19, with the expectation of starting human trials in June.

Kevzara belongs to a class of drugs called interleukin-6 (IL-6) inhibitors that could help regulate a dangerous overreaction to the virus by the body’s immune system called a “cytokine storm,” which may be triggering the respiratory distress seen in severe COVID-19 cases.

Early analysis of the study showed Kevzara rapidly lowered levels of C-reactive protein, a marker of inflammation. However, the companies reported negative trends for most “severely” ill patients given the drug, while there were positive trends in the critically ill group.

Researchers were looking for reductions in risk of death and need for a ventilator, as well as clinical improvements such as ability to come off oxygen therapy or be discharged from the hospital. Those who received the higher tested dose of Kevzara (400 milligrams) appeared to fare better among the critically ill group.

Dr. Kevin Tracey, head of research at New York hospital group Northwell Health which participated in the trial, cautioned against drawing strong conclusions on the use of IL-6 inhibitors for COVID-19.

Different compounds that work similarly could be more effective, he said in a phone interview, noting that rheumatoid arthritis treatments from another class of drugs may help one patient with the condition but not another.

“Scientifically, we don’t know why,” he said. “I wouldn’t draw any conclusions negatively or positively until the results of the randomized clinical trials are in of the particular agents.”

Also on Monday, French researchers said Roche Holding AG’s IL-6 inhibitor Actemra significantly reduced the risk of death and the number of patients needing a ventilator in a study 129 COVID-19 patients. However, full data from that study has not yet been released or peer reviewed.

Regeneron shares, which have risen nearly 50% so far this year, closed down 3.3% at $547.52.

(Reporting by Manas Mishra and Saumya Sibi Joseph in Bengaluru; and Michael Erman in New York; Editing by Ramakrishnan M. and Bill Berkrot)