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An experimental rheumatoid arthritis drug being developed by GlaxoSmithKline failed to show a significant benefit in hospitalized patients with Covid-19, the drug maker said Thursday.

However, patients older than 70 were more likely to be free of respiratory failure, a result that GSK plans to test in a new cohort of the study.

“The bottom line is we’re doing a confirmatory cohort study,” said Mark Layton, a medical development lead at GSK. “We accept that subgroups can be misleading.”

“At this point you can draw no conclusion other than it is potentially worthy of further study,” said David Batinelli, the chief medical officer of Northwell Health, who was not involved in the study. With any effective therapy, he said, the biggest benefit would be in patients who are at highest risk.

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The study included patients who needed assistance breathing, including high-flow oxygen, in which air pressure helps get it into the lungs, and mechanical ventilation. Researchers enrolled 800 patients and randomly assigned them to receive either a single dose of the drug, otilimab, or placebo. The main measurement of benefit was the number of patients who were alive and not in respiratory failure.

Overall, 4.9% more patients met this criterion — a result that was not statistically significant. Among the 180 patients who were over 70 and received otilimab, 18.5% more were free of respiratory failure, and it appeared they lived longer, too.

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But subgroup analyses can be deceiving. GSK’s Layton argued that the science of immunosenescence — the way the immune system becomes dysregulated with aging — fits well with the result. Covid, he said, may cause the immune system to overreact particularly in aging people.

Otilimab is a monoclonal antibody against the granulocyte macrophage colony-stimulating factor, or GM-CSF, which stimulates the production of white blood cells. The drug is also being tested in rheumatoid arthritis.

A small biotech, Humanigen, is testing another anti-GM-CSF antibody, lenzilumab, also in hospitalized patients. Humanigen said Jan. 29 that it expects results from its study, in 520 patients, in March.