Arena Falls 28% on Drug Trial

By DAVID BENOIT

Arena Pharmaceuticals Inc. shares fell 28% after it said its trial for an obesity treatment met its primary goal, but one result on weight loss fell short of an FDA guideline.

Analysts said the study should prove it can be approved by the Food and Drug Administration.

The San Diego, Calif., company said its two-year study on lorcaserin met all primary goals and showed the drug was well-tolerated by patients. The drug showed statistical significance in weight loss compared with patients on a placebo. After 12 months, patients on lorcaserin lost an average of 5.8% of body weight, or 12.7 pounds, compared with 2.2%, or 4.7 pounds, for the placebo group.

The difference of 3.6 percentage points was short of the 5% difference the FDA seeks.

Shares fell $1.27 to $3.23 apiece in 4 p.m. Nasdaq Stock Market composite trading.

The company said the 3.6 percentage-point figure wasn't the most important, saying the percentage of patients who lost 5% or more of their body weight was the first goal, and that did beat the FDA's benchmark. The study showed that 48% of lorcaserin patients lost 5% or more of their body weight, compared with 20% of the placebo group.

Write to David Benoit at david.benoit@dowjones.com