Even though diet pill rimonabant (Acomplia / Zimulti) remains stalled at the FDA, and in the next few years may face stiff competition from several drugs already in or moving into phase III trials, a leading research firm forecasts that Acomplia will be the clinical gold standard for treating obesity in 2010.

Decision Resources, Inc., in a new report issued March 19th, predicted that rimonabant's side effects of anxiety and depression in some patients "will not stop Acomplia's rise to the top," with it replacing prescription drug Xenical (orlistat) as the top selling diet drug.

Decision Resources said it based its findings on a survey of more than 3,000 endocrinologists with large practices as well as on its own analysis and comparisons of the key clinical attributes of current and emerging obesity therapies.

"Besides greater weight reduction and additional cardiovascular benefits, Acomplia promotes a longer period of weight maintenance and greater waist circumference reduction," said Decision Resources analyst Nancy Li.

"Although Acomplia is contraindicated in patients with depression and may cause side effects of anxiety and depression in certain subpopulations, its lack of upsetting GI side effects is a welcome difference for patients who have tried Xenical," Li added. "In addition, Acomplia is dosed more conveniently."

Interestingly, DRI's analysts appeared to focus primarily on two lesser known drugs -- Arena Pharmaceutical's Lorcaserin (APD356) and Alizyme's Cetilistat (ATL-962)-- as potential significant competitors to Acomplia in the immediate years ahead.

Arena has a two-year Phase 3 trial of lorcaserin underway that is expected to enroll 3,000 overweight and obese patients at about 100 centers in the United States. Lorcaserin stimulates the 5-HT2C serotonin receptor, located in the hypothalamus, which helps regulate fullness and influences the metabolic rate.

Alizyme is preparing to launch phase III trials for Cetilistat after completing an extensive Phase I and Phase II clinical development program. Cetilistat is a gastrointestinal lipase inhibitor which blocks fat digestion and thus absorption, but with far fewer gastrointestinal adverse events than Xenical.

In the report, DRI forecast that Lorcaserin would launch in 2009 and have peak year sales of only $250 to $500 million. It forecast that Cetilistat would launch in 2010 and have peak year sales that would only be half of Lorcaserin.

Curiously, the report gave no consideration to the possible competition posed for Acomplia by two other CB-1 receptor antagonists that Merck and Pfizer have in Phase III trials. If either the weight-loss performance or side-effect profile of one of these drugs is better than rimonabant, it could have a major impact on Acomplia sales.