Oct. 24 (Bloomberg) -- The failure of Sanofi-Aventis SA's Acomplia weight-loss pill threatens the development of new medicines to fight obesity.

The suspension of Acomplia sales yesterday in Europe struck a knockout blow to the most promising drug to tackle the modern health scourge since fen-phen, the combination treatment prescribed 6 million times before it was recalled for deadly side effects more than a decade ago. Acomplia failed to win the backing of a U.S. advisory panel last year.

Drugmakers from New York to Tokyo have been searching for weight-loss treatments as the world's 1 billion overweight and obese people face greater risk of heart attacks, strokes and diabetes. Companies developing obesity medicines may struggle to find partners to share costs and sales as the products become more of a regulatory gamble, analysts said.

``It might temper the naive enthusiasm of the drug companies to exploit these markets,'' said Erik Millstone, a science policy professor at the University of Sussex in England who coordinated a European Union study of different ways to fight obesity. ``In my 2006 study, it was striking how widespread the view was that using drugs to prevent obesity was seen as unacceptable.''

The London-based European Medicines Agency, which approved Acomplia in 2006, recommended the suspension of sales because the drug's risk of psychiatric side effects outweighed any benefits.

The regulators' action against Acomplia won't stop the drugmakers from trying to find a new obesity product, Millstone said today in a telephone interview. ``It depends on the drug: how it performs and what its safety profile is,'' he said.

`Dead in Water'

Acomplia was the first of a class of drugs called selective cannabinoid receptor CB1 antagonists that work by blocking hunger signals in the brain. Merck & Co. said earlier this month that its experimental treatment taranabant, in the same class of medicines as Acomplia, won't make it to market because it makes people depressed and irritable.

``The CB1 antagonists are pretty much dead in the water for obesity,'' said Jacob Plieth, an analyst at Edison Investment Research in London who wrote a May report on obesity drugs called ``Fat Chance.'' ``This could be the death knell for broadly indicated obesity drugs. We don't really know.''

NeuroSearch A/S has been seeking a development partner for its experimental obesity treatment tesofensine. The drug, which is in a different class from Acomplia, maintains higher than normal levels of three brain chemicals. That prolongs the pleasure people get from eating and makes them feel full earlier.

The European agency's recommendation sent Sanofi down for a second day. The French drugmaker fell as much as 8.6 percent in Paris trading and NeuroSearch dropped to the lowest level in more than three years in Copenhagen.

Roche's Xenical

``The regulators haven't changed the regulations but companies may think it will be more difficult since we're seeing the failure of Acomplia,'' said Peter Andersen, an analyst at Jyske Bank who cut his price target for NeuroSearch today to 250 kroner from 340. ``There is negative sentiment around obesity drugs, and this is a new market so the risk is already high.''

The drug industry hasn't introduced a new diet pill since 1998, when Switzerland's Roche Holding AG received European approval to sell Xenical. It won U.S. approval in 1999.

Xenical was also hailed as a potential blockbuster, with analysts predicting annual revenue of more than $1 billion when the drug was introduced. The medicine, hampered by embarrassing side-effects such as some patients' inability to control bowel movements, generated sales of 632 million Swiss francs ($547.5 million) last year.

Still, European regulators said yesterday that the active ingredient in Xenical, orlistat, could be sold over-the-counter by GlaxoSmithKline Plc as Alli. The product can be available as a non-prescription treatment in 60 milligram doses, the EMEA said.

Drugs in Development

Some drugmakers have abandoned potential obesity treatments rather than risk failure to win approval. Pfizer Inc., the world's biggest drugmaker, stopped early-stage work on obesity treatments as part of an overhaul of its research department.

Alizyme Plc, which has licensed its cetilistat obesity drug to Japan's Takeda Pharmaceutical Co., fell as much as 5 percent in London trading. Takeda, Asia's biggest drugmaker, decided to start the last of three stages of studies needed for approval, Cambridge, England-based Alizyme said last month.

Shionogi & Co., the Japanese maker of the Crestor cholesterol pill, is also working on an obesity treatment, called S-2367, that's in the second of three phases of research generally required for regulatory approval.

In the U.S., Amylin Pharmaceuticals Inc. is testing its pramlintide combination therapy for obesity. Arena Pharmaceuticals Inc., based in San Diego, said in March that its experimental obesity pill, lorcaserin, passed a test showing it doesn't damage heart valves like fen-phen.

`Time Will Tell'

``There is certainly a chance that big pharma will decide that obesity is not an indication worth pursuing,'' Edison Investment's Plieth said. ``Only time will tell.''

Sanofi's withdrawal of Acomplia in Europe may plague its plans to reapply to the FDA in the fourth quarter of 2009, this time for approval to treat diabetes. Sanofi has tried to refashion Acomplia by testing the drug as a treatment for conditions made worse by being overweight, such as lipid disorders and hardening of the arteries.

AstraZeneca Plc, the U.K.'s second-biggest drugmaker, is developing two Type 2 diabetes treatments in the same drug class as Acomplia. AZD-2207 is in the second phase of testing and AZD- 1175 is in the first stage. The drug class may be salvaged if shown to work in diabetes, Plieth said.

To contact the reporters on this story: Frances Schwartzkopff at fschwartzkop@bloomberg.net; Trista Kelley in London at tkelley2@bloomberg.net

Last Updated: October 24, 2008 08:38 EDT