Efforts by US company Cephalon to expand the uses of its epilepsy drug Gabitril to include generalised anxiety disorder have hit a major snag.

Cephalon said yesterday that a Phase III trial of Gabitril (tiagabine) in GAD patients failed to show an improvement in efficacy compared to placebo, driving its share price down over 4% in after hours trading yesterday.

The company said it would "conduct a complete analysis of the data to assist in its evaluation of future clinical development plans for Gabitril in other therapeutic areas."

Gabitril has been approved since 1997 for use in addition to other medications to treat partial seizures in epileptic patients aged 12 years and above, but approval in GAD would have dramatically increased the number of patients eligible to receive the drug. The company had been hoping to gain approval for the new indication in the middle of next year.

Meanwhile, the US Food and Drug Administration last year added a warning to Gabitril’s labelling to guard against off-label use of the drug, after it was linked to seizures in non-epileptic patients. Cephalon licensed Gabitril from Sanofi-Synthelabo (now Sanofi-Aventis) in 2002.

The trial is the latest in a string of setbacks for Cephalon, including a decision by a US FDA advisory panel to turn down its application to market attention deficit hyperactivity drug Sparlon (methylphenidate) in March, and a delay to the firm’s application to market sleep disorder drug Nuvigil (modafinil) in May while labelling is agreed with the agency.

On the plus side, the firm won approval for alcoholism treatment Vivitrol (naltrexone) in April, and is also waiting for a verdict on its cancer pain relief product FEBT by the end of the month.