Shares in US biotech Cephalon fell nearly 5% yesterday after the company was accused of acting unlawfully in its promotional activities for Actiq, a lollipop formulation of the opioid painkiller fentanyl.

Actiq is a major seller for Cephalon, providing the larger portion of the firm’s total pain franchise sales which reached $212 million in the third quarter of this year, up 40%.

The drug accounted for a third of the company's $1.2 billion in sales in 2005, but is likely to be hit next year by the launch of a generic rival developed by Barr Laboratories, and Cephalon is frantically trying to migrate Actiq users to its recently-launched Fentora product to lessen the impact.

The product is indicated for the treatment of breakthrough pain in cancer patients, but state authorities in Connecticut, USA, believe Cephalon has illegally promoted it for off-label use in other conditions requiring pain relief. In the USA, doctor are free to prescribe drugs off-label provided there are legitimate grounds for doing so, but companies are prohibited from promoting such uses.

The findings of the two-year investigation included that the company had set unrealistic sales targets for Actiq that could not have been met from use only in breakthrough pain. The probe also extends to Cephalon’s marketing practices for narcolepsy drug Provigil (modafinil) and Gabitril (tiagabine) for epilepsy.