The Bad News is Out on Sanofi-Aventis' Weight Loss Drug

Jun.12.07 | About: Sanofi (SNY)

The FDA briefing documents for Wednesday's discussion of sanofi-aventis' (NYSE:SNY) Accomplia / Zimulti (rimonabant) have been posted, and they're an interesting read indeed. As everyone in the industry knows, this drug was once looked on as the next potential record-breaker, and writing the first part of this sentence in that verb form tells you a lot about what's happened since. It's the first antagonist targeting the cannabinoid CB-1 receptor, and at one point it looked like it was going to make people lose their excess weight, shed their addictions, and, for all I know, refinance their mortgages.

But then the delays hit in the US - long, long ones, delays which made fools of everyone who tried to predict when they would be over. And the drug meanwhile made it to market in Europe, where it has very quietly done not very much.

Now we may be seeing some of the reasons for the FDA'a "approvable" letter over a year ago. It's not efficacy - the FDA's briefing summary states that:

Rimonabant 20 mg daily vs. placebo was associated with statistically and clinically significant weight loss. Rimonabant 5 mg daily vs. placebo was associated with statistically significant but clinically insignificant weight loss. . .rimonabant 20 mg daily vs. placebo was associated with a statistically significant 8% increase in HDL-C and a statistically significant 12% decrease in TG levels. There were no significant improvements in levels of total or LDL-C in the rimonabant 20 mg daily vs. placebo group. . .rimonabant 20 mg compared with placebo was associated with a statistically significant 0.7% reduction in HbA1c in overweight and obese subjects with type 2 diabetes taking either metformin or a sulfonylurea.

Not bad - just the sort of thing you'd want to go after the whole obesity/diabetes/cardiovascular area, you'd think. But the problem is in the side effects, and one in particular:

The incidence of suicidality – specifically suicidal ideation – was higher for 20 mg rimonabant compared to placebo. Similarly, the incidence of psychiatric adverse events, neurological adverse events and seizures were consistently higher for 20 mg rimonabant compared to placebo. . .

They're also concerned about other neurological side effects, and seizures as well. The seizure data don't look nearly as worrisome, except in the obese diabetic patients, for whom everything seems to be amplified. And all of this happens at the 20-mg dose, not at the 5 (which doesn't do much for weight, either, as noted above). And for those who are wondering, yes, on my first pass through the data, I find these statistics much more convincing than I did the ones on the Avandia (rosiglitazone) association with cardiac events.

I had my worries about rimonabant a long time ago, but not for any specific reason. It's just that I used to work on central nervous system drugs, and you have to be ready for anything. Any new CNS mechanism, I figured, might well set off some things that no one was expecting, given how little we understand about that area.

But isn't it good to finally hear what the arguing is about? Sanofi-Aventis has been relentlessly tight-lipped about everything to do with the drug. I can see why, after looking at the FDA documents, but this isn't a problem that's going to go away by not talking about it. The advisory committee meeting is Wednesday. Expect fireworks.