Experimental diet pill hopes to win FDA approval

Arena Pharmaceuticals and Eisai Co. have put their experimental diet pill back into clinical trials in hopes of gaining approval from the Food and Drug Administration (FDA). Qnexa, a combination of the weight loss drug phentermine and the antiepileptic medication topiramate (Topamax), was rejected by the FDA last fall because there was not enough data to measure the benefit/risk profile. The FDA also raised questions about early animal trials that showed the drug caused cancerous tumors in laboratory rats.

The latest clinical trial involves nearly 2,500 overweight and obese men and women. Each were randomly assigned to diet and exercise counseling alone or to counseling along with once-daily low- or high-dose Qnexa. The low-dose Qnexa contained 7.5 mg of phentermine and 46 mg topiramate, while the high-dose pill contained 15 mg of phentermine and 92 mg of topiramate.

After 56 weeks, patients on either dose of Qnexa had lost significantly more weight than those who only took part in the diet-and-exercise-counseling program. Patients on the low-dose of Qnexa lost an average of 18 pounds and patients on the high-dose of Qnexa lost an average of 22 pounds. Patients selected for the diet-and-exercise plan lost only an average of 3 pounds.

Additionally, patients taking Qnexa had reductions in their blood pressure, blood cholesterol levels, triglycerides, and blood sugar levels. The study also showed that the weight-loss seen in the first year of the trial was maintained in the second year of the trial.

Side effects were most often experienced in patients taking the higher dose of the medication, and included dry mouth, a feeling of “pins and needles,” constipation, insomnia, dizziness, and distorted taste. There was also an increased risk for depression and anxiety in patients taking Qnexa, and that risk was higher in patients taking the higher dose of the drug. There were no birth defects among the 34 women who became pregnant while taking Qnexa.

Currently, the weight-loss industry is underserved by adequate prescription drugs. Last fall the FDA also ordered the removal of the diet drug Meridia (sibutramine) because studies showed it increases the risk of serious cardiovascular problems. Another diet drug is orlistat, marketed in the U.S. as the prescription Xenical and the OTC Alli. The drug now carries a warning for severe liver injury.