Doctors around the world, trying to save seriously ill coronavirus patients, have been dosing them with rheumatoid arthritis drugs that can squelch immune responses. The theory was that many were dying because their immune systems went into overdrive, creating a fatal storm that attacked their lungs.

But now, preliminary results on treatments with one of these drugs, sarilumab, marketed as Kevzara and made by Regeneron and Sanofi, indicate that it does not help patients who are hospitalized but not using ventilators.

The rush to treat patients with rheumatoid arthritis drugs began with a tiny study in China in February. It involved just 21 patients, all of whom were hospitalized with Covid-19. All of the patients received a drug made by Roche, tocilizumab, that is very similar to sarilumab. The doctors reported that the patients’ fevers disappeared within days and, the doctors wrote, that “all other symptoms improved remarkably.” They ended on an optimistic note, writing, “Tocilizumab is an effective treatment in severe patients with Covid-19.”

Dr. George D. Yancopoulos, chief scientific officer of Regeneron, said the company had rushed to start a clinical trial of its drug in coronavirus patients. But he was not optimistic. Drugs like sarilumab and tocilizumab were specifically designed for arthritis, not Covid, he noted.