What happened

Shares of ChemoCentryx (CCXI) were crashing 46.5% lower as of 3:06 p.m. EDT on Tuesday. The huge decline came after the U.S. Food and Drug Administration (FDA) released briefing documents for an advisory committee scheduled to meet on Thursday to review the approval application for avacopan.

So what

As you might have guessed from the collapse of the biotech stock today, the FDA's briefing documents didn't look very good for ChemoCentryx. Instead, the documents raised significant doubts about the prospects for avacopan to win approval in treating anti-neutrophilic cytoplasmic autoantibody (ANCA)-vasculitis, an autoimmune disease that causes small blood vessels to swell.

Man wearing coat and tie holding blocks in his hand spelling FDA

Image source: Getty Images.

The FDA stated in the briefing documents that ChemoCentryx's study design on which its regulatory filing is based "raise questions about the interpretability of the data to define a clinically meaningful benefit of avacopan." That basically means that the agency doesn't put much stock in the clinical results for the experimental drug.

This shouldn't have been much of a surprise to ChemoCentryx, though. The FDA stated that it previously informed the company about many of its concerns about the design of the late-stage study for avacopan.

Now what

It's possible that the Arthritis Advisory Committee will still view ChemoCentryx's filing for avacopan in a positive light. That doesn't seem likely at this point, though, considering the strong language the FDA included in its briefing documents.

Even if the advisory committee recommends approval, the agency doesn't have to go along with that recommendation. ChemoCentryx could very well have to conduct another late-stage study to address the FDA's concerns.