Amylin Pharmaceuticals reported on Nov. 15th that patients in a 24-week phase II trial of its diet drug combining pramlintide and the hormone metreleptin lost an average of 12.7 percent of their body weight, and that weight loss continued all the way through the study.

The study found that pramlintide combined with metreleptin was significantly more effective in overweight and obese trial participants than those treated with pramlintide alone.

Pramlintide is a synthetic analog of amylin and it is the active ingredient in Symlin, a diabetes drug Amylin has on the market. Metreleptin is an analog of leptin, a signaling molecule that regulates energy metabolism and body weight.

“Amylin's finding that combination treatment with pramlintide and metreleptin led to over 12 percent weight loss in obese people marks a very important milestone for our obesity program,” said Christian Weyer, Amylin's executive director of clinical research.

While the the weight loss seems impressive, the big question -- which will remain unanswered until a longer phase III trial -- is whether it continues beyond six months, potentially making this a blockbuster obesity drug.

Because unless the weight loss turns out to be significantly greater than what can be achieved with oral drugs like rimonabant, orlistat, or one of the new drugs under development, the fact that Amlin's combination drug has to be taken via a twice-daily injection would appear likely to limit demand.