The experimental diet drug Qnexa -- which combines the diet pill phentermine and the active ingredient in Topamax (topiramate), a drug used to prevent migraines and treat seizures -- has produced impressive results in a small Phase II clinical trial.

In the 200-patient, double-blind, placebo-controlled clinical trial conducted by Duke University Medical Center, more than half of the 50 obese patients in the Qnexa treatment group experienced 10 percent or more total body weight loss during the 24-week trial.

"Importantly, the rate of weight loss for patients in the Qnexa group had not plateaued by the end of the study," a spokesperson for the drug's developer Vivus, Inc., reported. He also said Qnexa was well-tolerated with 92 percent of those taking it completing the trial.

"The weight loss observed in this trial is quite impressive," said Dr. Kishore M. Gadde, Director, Obesity Clinical Trials Program, Duke University Medical Center.

"Qnexa is being developed as a proprietary pharmaceutical treatment that incorporates the active ingredients from two previously approved products with demonstrated weight loss properties," said Wesley W. Day, Vivus Vice President, Clinical Development.

But while the two active ingredients in Qnexa may have been individually approved by the FDA, Qnexa is hardly likely to make it to market anytime soon.

Phentermine, which is continues to be sold as a diet drug, was part of the diet drug combination Fen-phen that was pulled from the market in the 1990s when the combination was found to contribute to heart valve damage.

As for topiramate, Johnson & Johnson's patent covers weight-loss as well as the other indications for which Topamax currently is sold. While Vivus obviously is hopeful of avoiding patent issues, it is by no means a certainty.

This trial involved 200 subjects, 159 women and 41 men with an average age of 40 and a mean body mass index (BMI) of 38. Each subject in the study received daily doses, consisting of Qnexa, a placebo, or one of the active ingredients. Subjects were asked to reduce caloric intake by 500 calories per day.

Primary and secondary efficacy measurements in the study all showed that Qnexa was significantly better than a placebo or either phentermine or topiramate alone.

" We believe that by combining the activity of each of these compounds, Qnexa simultaneously addresses the two main mechanisms that impact eating behavior," said Day. "Qnexa could be the first product to significantly affect both excessive hunger and the inability to feel satisfied.