Solvay and Wyeth have filed a new treatment for schizophrenia with the US regulators, which promises to be free of weight gain and other side-effects seen in patients taking existing treatments.

Bifeprunox is a partial dopamine agonist, a novel treatment for the condition which has been co-developed by Solvay and Lundbeck in Europe, with Solvay linking up with Wyeth to market the drug in North America.

The companies concede that bifeprunox may have a smaller mean effect in treating acute psychosis compared with existing atypical antipsychotics, but say it may be particularly well-suited for patients who experience side-effects on current therapy.

Leading atypical treatments, in particular Lilly's market leader Zyprexa, have been hit hard by evidence that they increase the risk of weight gain and diabetes in some patients.

In June 2005, Lilly settled out of court with around 8,000 claims from patients alleging Zyprexa caused them to develop diabetes.

Trials of bifeprunox suggest the drug does not cause the weight gain or raised cholesterol levels seen in older atypical treatments.

The drug has been submitted as a treatment for patients experiencing acute attacks of schizophrenia, as well as those whose condition is stable.

"One recent U.S. government-sponsored study, CATIE (Clinical Antipsychotic Trials of Intervention Effectiveness), showed a significant need for new treatment options, especially over the long-term," says Joseph Camardo, head of global medical affairs at Wyeth.

"We are pleased that our collaboration with Solvay Pharmaceuticals has resulted in an application with proposed indications for both initial therapy and maintenance, which is an important feature for an atypical antipsychotic."

Analysts predict bifeprunox will earn around $1 billion in peak sales, but will have to compete with another new schizophrenia drug expected to be launched in 2007.

Johnson & Johnsons paliperidone ER, an extended release follow-up to its blockbuster Risperdal, is currently the second biggest brand in the market behind Risperdal.

Another new entrant, Akzo Nobel and Pfizers asenapine is expected to gain approval in 2008, which analysts Datamonitor predict could be a market leader by 2015.

pharmafocus@wiley.co.uk