Max Nisen is a Bloomberg Gadfly columnist covering biotech, pharma and health care. He previously wrote about management and corporate strategy for Quartz and Business Insider.

FDA advisory panels can be pretty dull. They feature a numbing onslaught of data, ages of power point slides, and hours of jargon-dense back-and forth-between the FDA and drug companies. That wasn't the case for a review this week of drisapersen, a BioMarin Pharmaceutical drug for a rare, fatal disease called Duchenne Muscular Dystrophy, which nearly always affects young boys. It included moving testimony from patients and their parents. At one point, people trying to watch online overloaded the FDA's livestream. 

This was a more difficult vote than most for the FDA panel, particularly in front of people suffering from the disease. There's no approved therapy for the drug, and DMD is fatal, so families and patients accept a high level of risk for even a small benefit. There's been an intense lobbying effort to get approval.

On the Downslope
BioMarin's Duchenne Muscular Dystrophy drug looks like it's in trouble

But the panel was correct to vote in a way that makes final FDA approval, due by December 27, look less likely. Fifteen of 17 panel members said a large, late-stage study failed to show statistically significant improvement for patients, weakening better results in smaller, earlier studies. The review also noted serious doubts about the drug's safety. At one point, the leading FDA reviewer said that, even though there were no deaths during these early studies, the adverse reactions could be so severe that death is a risk.

These panels aren't binding, but the FDA generally follows their advice in making a final decision. There's still a chance the drug will be approved, but the prospects look far worse than they did a week ago. 

BioMarin shares fell 5 percent before the panel, after the FDA's long list of concerns about the drug were released last Friday. They were down as much as 1.5 percent on Wednesday, after being halted throughout the day of the review on Tuesday.

Almost exactly a year ago, BioMarin paid $680 million to acquire Prosensa, which developed the drug. GlaxoSmithKline had at one point partnered with Prosensa on the drug, but dropped out after disappointing clinical trial data. BioMarin's bet on Prosensa was seen as risky at the time, and those concerns now seem justified.

BioMarin has a deep pipeline of rare disease drugs. But losing drisapersen's potential revenue will hurt. The high prices commanded by such "orphan drugs," which treat rare and previously untreated diseases, would have made this drug a big moneymaker, despite an initial patient population in the low thousands in the U.S. Writing off that pricey Prosensa buyout will sting, too. 

The Last Drug Standing?
After a disheartening FDA review of a BioMarin drug, Sarepta's price jumped

The one silver lining for patients here is that drisapersen isn't the only option. A company called Sarepta has a DMD drug of its own, which the FDA is set to rule on in February. The intensity of the FDA's scrutiny of BioMarin's drug is a worrisome sign for the prospects of Sarepta's drug. But Sarepta shares are up 40 percent since the initial negative review of BioMarin's drug came out last week.  

So far, Sarepta's drug looks safer than drisapersen. And Sarepta claims it is more successful at producing dystrophin, a muscle-building protein lacked by those suffering DMD. Its data are still early and based on a small sample. But the FDA may have a harder time sending a second medicine back to the drawing board if it rejects BioMarin's drug.  

If Sarepta winds up with the only approval for a DMD treatment, then its profits could be enormous.  

Investors have flocked to orphan drugs after companies such as Vertex, which makes Kalydeco and Orkambi for cystic fibrosis, have turned small patient populations into blockbusters. Such drugs get an accelerated review process and the ability to run smaller clinical trials than most drugs, and they have enormous potential pricing power. They might be less risky in some ways than chasing the next drug for, say, Alzheimer's, which is competitive, has a decades-long history of research failures, and for which a drug would have to demonstrate effectiveness and safety across a large patient population. 

But as BioMarin is finding out, orphan drugs are not sure bets, either.  

This column does not necessarily reflect the opinion of Bloomberg LP and its owners.

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Max Nisen in New York at

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