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The FDA committee that will be looking over Arena's (NASDAQ:ARNA) lorcaserin for weight loss has released its briefing information, and there were some nasty surprises therein. A memo states that the drug did not satisfy the mean efficacy requirements that the FDA has laid down for obesity therapies, and satisfied the categorical efficacy one "by a slim margin".

Well, that was known. I said as much back in May of last year, and didn't the Arena fans ever give me an earful about it. What wasn't apparent was the two-year rodent tox. The briefing document raises questions about the number of malignancies that showed up in these rats, and that's not good. The safety profile of any drug in this area has to be very clean, especially if the efficacy is borderline.

As for the big worry about any serotinergic compound in this area, 5-HT2b heart valve trouble, the briefing document isn't too reassuring there, either. The FDA staffers note that the company didn't run a positive control in the animal models, and didn't look at proliferative markers during the human clinical trials. They conclude that "the FDA has not definitively concluded that lorcaserin is devoid of valvulopathy-related cardiac effects in animals".

Frankly, I think that the tox/efficacy combination is likely to sink the drug's approval chances. There are other problems, but this is the big one. The market seems to be agreeing - Arena's stock was getting hammered Tuesday. I look forward to hearing from the various people who were after my hide about this.

Source: Arena's Weight Loss Drug in Trouble