Arena Drug Aids Weight Loss, a Little

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SAN DIEGO (TheStreet) -- Arena Pharmaceuticals(ARNA Quote) may want to think about tweaking the formula for its experimental weight-loss drug lorcaserin -- like adding a treadmill to the mixture.

That's because lorcaserin, on its own, isn't helping obese patients lose much weight, according to results from a second pivotal phase III study dubbed "Blossom" released Friday.

Arena is competing against Orexigen Therapeutics(OREX Quote) and Vivus(VVUS Quote) to develop a new obesity drug.

Patients taking lorcaserin twice a day lost an average of 5.9% of their body weight after one year, compared with patients on a placebo who lost 2.2% of their body weight -- a placebo-adjusted difference of just 3.1%.

The result, while statistically significant in favor of lorcaserin, doesn't come close to the 5% placebo-adjusted weight loss benchmark that many doctors believe is clinically meaningful for obese patients.

Measured another way, 47% of lorcaserin patients lost at least 5% of their body weight compared with 25% of placebo patients in the Blossom study.

The Food and Drug Administration approval guidelines call for a weight-loss drug to "approximately double" the percentage of patients losing 5% of their body weight. Whether or not lorcaserin meets this FDA requirement in the Blossom study depends on the definition of "approximately."

For its part, Arena executives hailed the Blossom results as positive and said the data confirm the previous results, also positive, from the first phase III study of lorcaserin, known as Bloom. Arena plans to file lorcaserin for approval with the FDA in December.