The FDA wants to pull its approval of a drug. It’s not so easy.

In May 2021, the US Food and Drug Administration released a lengthy briefing document on an experimental medication for a rare autoimmune form of vasculitis that often damages the kidneys and lungs. The agency was on the fence about whether to approve the treatment, and it wanted an independent advisory committee to weigh in. Among the questions at hand: Was the drug meaningfully better than existing therapies? Participants in the study, which had been conducted by the California biotechnology company ChemoCentryx, did appear to have slightly higher rates of symptom remission after one year. But according to the FDA, it was hard to interpret the results because the study’s design had been less than optimal. Some advisory committee members expressed a similar view. The effect of the drug, said one, “is just not well verified by this study.” At the same time, many patients, and some physicians, saw in the data a potentially helpful medication, one that might lessen patients’ reliance on steroids, which are highly effective but often cause severe side effects.