FDA staff question effectiveness of Arena, Eisai's obesity drug lorcaserin

FDA staff said Tuesday that Arena Pharmaceuticals and Eisai's experimental weight loss drug, lorcaserin, met one of the agency's effectiveness standards "by a slim margin," but concerns remain about the drug's safety. Arena shares fell as much as 37 percent on the news.
In documents released ahead of an advisory panel meeting Thursday, Eric Colman, deputy director of the FDA’s Division of Metabolism and Endocrinology Products, noted that lorcaserin did "satisfy the categorical efficacy criterion" of helping at least 35 percent of patients lose at least 5 percent of their weight.
However, the study results "did not satisfy the guidance’s mean efficacy criterion," where the difference in weight loss between patients treated with the drug compared to patients in the placebo group be different by at least 5 percent. In the BLOOM trial, patients treated with the drug lost an average of 5.8 percent of their body weight compared with 2.2 percent body weight loss in the placebo group. The agency noted that a product is considered effective if it meets at least one of the criteria after one year of treatment.
FDA staff also noted that studies of the lorcaserin in rodents demonstrated there was an excess of breast tumours among those dosed at 7 times higher than the proposed clinical dose for humans, but said that no such imbalance in reports of cancer was observed among the more than 7000 patients treated with lorcaserin in late-stage clinical trials. The panel will be asked to vote on whether it thinks the benefits of lorcaserin outweigh the potential risks "when used long-term in a population of overweight and obese individuals."
Commenting on the documents, Hapoalim Securities analyst, Jon Lecroy, said that "knowing the drug doesn’t work that well, I knew the safety concerns would be looked at extremely closely," but said that "the big surprise to us here is the cancer" risk.

Reference Articles
Arena’s diet pill works by a ‘slim margin,’ FDA says - (Bloomberg)
FDA questions safety, effectiveness with diet pill - (MSN Money)
FDA: Arena's weight-loss drug lorcaserin meets one standard (free preview) - (The Wall Street Journal)
Arena tanks on drug safety concerns - (TheStreet.com)
Arena obesity drug was effective by ‘slim margin,’ FDA staff raises rat concern; shares tumble - (Xconomy)

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