UK drugmaker Shire said yesterday that the US Food and Drug Administration has not yet ruled on a Citizen’s Petition it filed, seeking to block generic competition to its attention deficit hyperactivity disorder (ADHD drug Adderall XR.

Shire filed the petition last October, asking the FDA to require would-be generic manufacturers of the drug to carry out studies to make sure that their rival products have the same pharmacokinetic profile as the innovator drug, through more rigorous bioequivalence testing or additional clinical trials.

A spokesperson for the UK firm told PharmaTimes recently that it wants generics to undergo the same plasma concentration time curve studies that the FDA ruled were the only substitute for a clinical efficacy trial when it sought approval of Adderall XR.

This is not the first time that a company selling a once-daily treatment for ADHD has used the Citizen's Petition route in the USA to try to block generic competition. In 2004, Johnson & Johnson adopted this strategy for its Concerta (methylphenidate) product, again asking that generic companies be asked to supply more robust bioequivalence data in order to secure approval.

Shire has been busily defending Adderall XR from cut price generic competition as it tries to reduce its reliance on the product, its top seller with sales of $730 million in 2005, through the launch of new products.

The UK firm filed a patent infringement lawsuit against Teva last month after it filed for approval of a copycat version of the drug in the USA, and is also suing Barr Laboratories on similar grounds. Meantime, Shire has forged a settlement with another firm, Impax Laboratories, which could prevent the generics firm launching a rival product until 2010.