Arena Pharmaceuticals Inc.'s Plan to Win the Obesity Drug War

Considering the number of obese Americans -- 35% of the entire U.S. adult population, according to the Centers for Disease Control and Prevention -- obesity-drug makers haven't come close to reaching their potential. Arena Pharmaceuticals reported $45 million in net sales of Belviq last year, and VIVUS reported a similar level of Qsymia sales.

Takeda launched Orexigen's Contrave a few months ago; while it is off to a faster start than the two competing drugs and increased the total market, prescriptions of Contrave still trail those of Belviq, so it's not exactly on path to being a blockbuster this year.

The companies obviously must do something to kick-start the market. The good news is Arena Pharmaceuticals has a plan. We'll have to wait and see how it works out, though.

Arena and marketing partner Eisai are developing an extended-release versionof Belviq -- called Belviq XR -- that only has to be taken once daily instead of twice daily like the current version. In one clinical trial, the companies showed the two versions' drug concentration was equivalent, and a second trial demonstrated the new version was safe and equivalent whether taken on an empty stomach or after eating.

The press release was light on details, but it seems safe to take the companies' word for it and assume the Food and Drug Administration won't have any problem with the equivalency data. The application for Belviq XR should be filed later this year, putting a potential FDA approval next year.

No doubt once-daily dosing will be more convenient, but is taking an extra pill a day really an impediment to use of Belviq? I'd guess not. To really get doctors and patients excited about an obesity drug, companies need to find one that is more effective.

Or maybe twoArena's better shot at a blockbuster comes from combining Belviq with phentermine, a generic obesity drug whose claim to fame is being the innocent party in the Fen-Phen heart valve side effect that got fenfluramine pulled off the market.

Belviq works in much the same way as fenfluramine; both drugs act on serotonin receptors to make patients feel full, thus reducing appetite. But Belviq was specifically designed to not work on the serotonin receptors in the heart valve to avoid the damage caused by fenfluramine.

In a pilot trial,Arena and Eisai testedthe combination of Belviq and phentermine on 238 patients, and the combo appeared as safe as Belviq when measuring side effects associated with the serotonin receptor. Measurements of blood pressure and heart rate weren't as good for the combination as they were for Belviq, but phentermine is known to negatively affect those measurements, so the poorer results aren't too surprising.

Given that the trial only lasted 12 weeks, it's hard to draw any conclusions about safety other than the combination appears safe enough to conduct a larger, longer clinical trial. The companies said they would meet with the FDA "around midyear" to discuss how to proceed with agency approval of the drug combination.

If Eisai and Arena can prove the combination is safe in larger trials, its weight-loss numbers, which are greater than those of Belviq alone, are likely to garner more interest from patients and doctors. Patients on the combination lost 7.3% or 8.7% of their body weight, depending on whether they received phentermine once or twice a day, compared to just 3.8% of body-weight loss for patients taking only Belviq.

The other measurement of weight loss the FDA likes to see -- percentage of patients who lost at least 5% of their body weight, which is considered meaningful for improving health -- was also considerably better for the combination. A whopping 84.2% of patients taking phentermine twice daily and Belviq lost at least 5% of their body weight, compared to just 33.3% of patients who only took Belviq. The once-daily phentermine plus Belviq group came in at a solid 68.2% of patients losing 5% of their body weight.

It should be noted that the weight loss data is only for patients who completed the study -- adding in the dropouts would likely decrease the weight loss -- but the FDA will assess the drug based on all the patients in the trial. If substantially more patients taking the combination drop out compared to the control group, the weight loss effect will be mitigated.

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