Diet drug Acomplia (rimonabant) users might want to pay close attention to an issue that developer Sanofi-Aventis is now facing the need to address more openly with regulators (if not dieters): If you want to keep off the weight you lose on Acomplia, you need to take the drug daily for the rest of your life.

Marc Cluzel, senior vice president for scientific and medical affairs of Sanofi, told analysts Sanofi withdrew its application to sell rimonabant in the United States because it felt there would not be adequate time before July's expected FDA decision to discuss issues raised by the FDA advisory panel linked to "duration of treatment."

In the Phase III clinical trials for Acomplia, patients who were on rimonabant for a year lost up to 10 percent of their body weight. But while those who continued on Acomplia for a second year maintained their weight loss, those switched to a placebo tended to quickly regain the weight.

That would strongly suggest that to keep weight lost while taking Acomplia from returning, patients would need to continue taking rimonabant indefinitely -- a point the FDA advisory panel picked up on in unanimously concluding that not enough long-term safety data had been submitted by Sanofi.

"There was general agreement among the committee that there needs to be more long-term data; the concern being that of having limited 2-year study data being used to assess a drug that would be used long-term," the FDA advisory panel said in the minutes of the June meeting.

Cluzel, in his comments on the advisory panel statement, said "I think the review committee took recognizance at this time that obesity is a chronic disease, and I think that is the spirit of the comment.

"With any kind of chronic disease, when you stop your treatment -- in fact, whether you are taking an antihypertensive drug, when you stop your treatment you get back your high blood pressure," Cluzel said.

"I think what emerged from the data with Acomplia / Zimulti is really the chronicity of the obesity treatment," Cluzel concluded. "This is really a disease which is a chronic disease. We thought that we had not enough time after the meeting to discuss . . .the duration of treatment requested for a chronic disease like obesity."