UK drugmaker Shire Pharmaceuticals has settled litigation with generics company Impax Laboratories over its bid to launch a generic version of Adderall XR (mixed amphetamine salts), Shire’s drug to treat attention deficit hyperactivity disorder.

Impax has accepted that three US patents covering Adderall XR are valid and enforceable and, in return, Impax will be able to sell its generic version of Shire's top-selling drug "no later than January 1, 2010," in the USA, according to the settlement agreement.

Shire said Impax would pay it a royalty on sales of its planned generic forms of Adderall XR, which had sales of $166 million in the third quarter of 2005. If another generic reaches the market in the interim, Impax may be permitted to enter the market as Shire's authorised generic, said the UK firm.

The settlement also includes a licensing deal in which Shire will pay Impax to promote its epilepsy drug Carbatrol (carbamazepine) in the USA for three years, beginning around July.

Discussions with another would-be generic Adderall XR seller, Barr Laboratories, are continuing, said the firm, with a pretrial conference scheduled for March 10. A settlement with Barr has also been expected, according to analysts.

In a separate statement Shire said Teva Pharmaceuticals, another generics group that is trying to make a copycat version of Adderall XR, has expanded its marketing to include an additional 25mg dose of the drug in addition to its already-filed 10mg and 30mg dosages. The UK firm said it was reviewing the application.