An experimental drug for the treatment of obesity, APD356, reportedly produced encouraging results in a relatively small four week clinical trial, according to a statement released by Arena Pharmaceuticals, Inc.

Arena said that over the 28 day period of the Phase II trial, study participants taking a 15 mg dose of APD356 lost an average of 2.9 pounds, compared with 0.7 pounds for those in a control group receiving a placebo.

APD356 activates serotonin receptors in the hypothalamus area of the brain, an area known to play an important role in regulating food intake and metabolism.

The new pill thus bears some similarities to the diet combination of fenfluramine and phentermine (fen-phen), in that fenfluramine also worked by increasing the amount of serotonin in the brain in a way that reduced appetite.

But that combination of two medicines damaged the heart valves of some of the people who took it, and fenfluramine was withdrawn from the market and drugmaker Wyeth ultimately set aside $21 billion to pay for settlements related to the drug.

Arena contends that fen-phen hit more brain receptors than necessary, and that the heart valve damage did not show itself to be a problem in this initial test.

Patients were assessed by echocardiogram upon enrollment, and were scheduled for follow-up echocardiograms at 29 and 90 days after receiving their first dose.

"There was no apparent drug effect on the heart as assessed by Day 29 echocardiograms," the company announced. "Post day 29 echocardiograms are pending."

"The results of this trial are very supportive of further study and provide hope that obese individuals could have a new therapeutic option in the future to help control their weight in an effective, safe and controlled manner," said Dr. Steven Smith, lead investigator in the trial.

This Phase 2 trial of APD356 enrolled 352 obese volunteers, with a body mass index (BMI) of between 30 and 45, at 24 clinical sites in the United States. The patients, 80 percent of whom were women with an average age of 40, were randomized into four groups to compare doses of 1, 5 and 15 mg of APD356 versus a placebo.

The trial protocol provided that patients should maintain their normal diet and level of activity, but required that patients abstain from consuming alcohol.

While the researchers described the weight loss by patients on the highest dose of APD356 as "clinically meaningful," they said no statistically significant weight loss was observed in the 1 mg or 5 mg groups.

Arena intends to use the results of the trial to support its search for a corporate partner for the drug and to begin a Phase IIb trial, which will enroll about 300 to 400 patients and test the drug over a three-month period.