GlaxoSmithKline has suffered a setback with the news that US regulators have rejected the antidepressant gepirone ER, which the UK drugs giant licensed from Fabre-Kramer Pharmaceuticals earlier this year.

The US Food and Drug Administration has issued a not approvable letter for the extended-release tablets, which had been submitted to the agency for the treatment of adults with major depressive disorder. The companies noted that they are “evaluating the response from the FDA to determine appropriate next steps”.

Gepirone ER has had a fairly rough ride in trying to get approved. Originally developed by Bristol-Myers Squibb, the compound was outlicensed to privately-held Fabre-Kramer which linked up with Akzo Nobel on the drug in 1999. Gepirone ER was first submitted for US approval in May 2001 by Akzo’s Organon unit Nobel but in April the following year, the FDA requested additional information on the filing. Then, later in the year, the drug, under the brand name Ariza, was delayed again after Organon took longer then expected to enrol patients into a clinical trial required to complete the dossier.

Again, in June 2004, the FDA requested an additional positive short-term trial in order to consider gepirone ER for approval. After this, Akzo abandoned development and returned all rights to Fabre-Kramer in June 2005 which in turn signed up GSK as a partner in February this year in a deal where financial details were not disclosed.

Meantime, Fabre-Kramer said that it had successfully conducted a trial in patients with major depressive disorder to respond to the FDA’s 2004 request and those results were submitted in May this year. However, the agency has now said that it is not impressed with the data raising doubts as to whether gepirone ER, a first-in-class 5HT1a agonist which had been touted as a blockbuster, will ever be approved.