U.S. regulators have rejected GlaxoSmithKline experimental drug gepirone ER for adults with major depression

The U.S. Food and Drug Administration (FDA) issued a not approvable letter for the extended-release tablets, gepirone ER which Glaxo had licensed from privately owned Fabre-Kramer Pharmaceuticals Inc in February, Europe's biggest drugmaker. The news is a blow to Glaxo, which needs new drugs to make up for pending patent expiries on key blockbusters and a recent slump in sales of its second-biggest seller, the diabetes pill Avandia, which has been hit by fears over a possible link to heart attacks.

Industry analysts had forecast that gepirone ER, if successful, could eventually have sold between $800 million (383 million pound) and $1.6 billion a year. But the product was always viewed as high risk, following a chequered history in development.

Akzo Nobel NV of the Netherlands had originally been developing gepirone ER with Fabre-Kramer but the Houston-based drug company bought back rights to the drug in June 2005 after Akzo abandoned development in the wake of two earlier rebuffs from the FDA.Despite these setbacks, Glaxo had hoped that gepirone ER might still be approved if it provided data from an additional positive clinical trial. Those extra results were submitted to in May 2007 but, in event, proved insufficient to sway the U.S. regulator.