Rimonabant rejection casts shadow over other obesity drugs

The US rejection of sanofi-aventis' obesity drug Zimulti (rimonabant) could scupper the sales of other weight loss drugs, while highlighting the difficulties of developing new anti-obesity medications.

According to Bank of America analysts, the bar for approval in the area of obesity had been raised. Other analysts have added that the FDA's ruling could also affect Pfizer and Merck & Co, both of which are developing drugs in the class known as CB-1 antagonists.

Leerink Swann analysts have said that they expect that large pharmaceutical companies developing CB-1s may now look more closely at their development programmes, adding that the outlook for the class was now in doubt.

With obesity now a worldwide health concern, treatments to combat the problem have been pushed through, only to cause serious side-effects. For example, 10 years ago Wyeth withdrew drugs in its fen-phen diet-pill combination over safety concerns. Also, Roche's Xenical (orlistat) did not produce the blockbuster sales the Swiss company had envisaged. Last week GlaxoSmithKline (GSK) launched alli, which is an OTC half-strength version of Xenical.

Morgan Stanley analysts said that little data were available on the products from Merck and Pfizer, but that studies done prior to human testing had pointed to evidence of toxicity. They described the FDA advisory panel's vote as being clearly a negative for the entire class.

As of December 2006, Pfizer's CB-1 antagonist, CP-945598, was one of eight drugs the company had in phase III testing for various conditions. It also has an extensive phase III programme, with a study of more than 4,000 patients planned, according to Leerink Swann analsysts.