Update: At the advisory committee meeting on Nov. 24, most panel members voiced doubts that the treatment was effective. A final FDA decision on drisapersen is expected by Dec. 27.

The fate of a drug to combat Duchenne muscular dystrophy may be in doubt after Food and Drug Administration staff raised serious concerns about the safety and effectiveness of the treatment. The assessment was contained in documents released on Friday in advance of an FDA advisory panel meeting next week to review BioMarin Pharmaceutical’s drisapersen, one of two new experimental medicines for DMD slated for regulatory review.

Listen to the Signal podcast: For boys with Duchenne, and two drug companies, a moment of shared hope

The FDA reviewers cited “life-threatening” side effects, such as a low blood platelet count and severe kidney damage. They also noted a lack of “substantial evidence” of effectiveness, pointing to a failed late-stage study and an inability to substantiate findings from a mid-stage study showing the mobility of boys taking the drug improved after a six-minute walking test. And they argued that the BioMarin drug did not seem to boost levels of dystrophin, the protein that is missing in boys with DMD and which is meant to be restored by the treatment.

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“The development program for drisapersen is extensive for a rare disease and exemplary,” the FDA reviewers wrote. “It is very disappointing that both clinical and biomarker data for drisapersen are inconclusive at this time.”

Read moreThe fight to save children’s lives — and reshape the FDA

The FDA staff stopped short of recommending that the agency not approve the drug. However, by reading between the lines, that seemed to be the take-away for most industry analysts. “In our view, FDA has made a very clear statement that there is no reason to approve drisapersen,” wrote R.W. Baird analyst Brian Skorney in an investor’s note.

Opinion remains divided, however, over what this review will mean for Sarepta Therapeutics, the company with a rival drug called eteplirsen that will be considered by an FDA review panel in January. Leerink analyst Joseph Schwartz thought it did not bode well for the competing treatment. But Needham analyst Chad Messer wrote the Sarepta drug has demonstrated greater safety and effectiveness — albeit in a randomized study of only 12 patients, four of whom received a placebo.

One surprise of the briefing documents was that the agency will not ask its panel of outside experts — none of whom are DMD specialists — to vote on whether the agency should recommend the drug. This should give the agency more leeway in its final approval decision as it struggles to balance the demands of families afflicted by the DMD with the need for scientific rigor.

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