UK company Shire Pharmaceuticals has attempted to block the approval of generic rivals to its top-selling Adderall XR (mixed amphetamine salts) drug in the USA by persuading the Food and Drug Administration to ask for additional testing data.

Shire has filed a Citizen’s Petition with the FDA which requests that the Agency require the generic companies 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.

Adderall XR, a once-daily line extension that has replaced Shire’s older instant-release formulation of the drug, is used for the treatment of children with attention-deficit hyperactivity disorder. It is Shire’s biggest-selling drug, bringing in $205 million dollars in the second quarter of this year, out of total company revenues of $425 million [[29/07/05f]]. The company maintains that its patents on the drug are valid out to 2018.

Shire said that it wants generics to undergo the same plasma concentration time curve studies that the FDA has 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. Last year, 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. To date no generic competition to this product has emerged, despite challenges from Mylan Laboratories and Andrx Pharmaceuticals.

“If a generic or follow-on drug sponsor is unable or unwilling to meet these criteria for establishing bioequivalence, the FDA should require an adequate and well-controlled clinical investigation demonstrating the clinical effectiveness and safety of the generic,” said Shire in a statement.

Several companies have filed for approval of generic versions of Adderall

XR’ including Barr Laboratories, Impax Laboratories, Colony Pharmaceuticals and Teva Pharmaceutical Industries. Shire has lawsuits ongoing against Barr and Impax, but recently divulged that it is negotiations with Barr that could lead to the latter company launching a licensed generic version of the drug before the 2018 patent expiry [[19/08/05a]].

Meanwhile, the lawsuit with Barr, the first company to file for approval of generic Adderall XR in the USA, is scheduled to come to court in January