Shire Pharmaceuticals has filed additional patent infringement lawsuits as it struggles to defend its top-selling product, the attention deficit hyperactivity disorder drug Adderall XR (amphetamine salts extended release) from generic competition in the USA.

In the latest action, the UK company has filed suit against two US generics companies - Barr Laboratories and Impax Laboratories - for infringing a patent on Adderall XR issued in July. Shire is already suing the two companies for infringing two other US patents in cases due to come to trials in January and February 2006, respectively [[10/01/03b]] [[05/01/04d]].

In addition to the patent lawsuits, Shire has also filed a Citizen’s Petition with the US Food and Drug Administration asking it to tighten up the criteria that generic manufacturers should have to meet to show that their generic versions of Adderall XR are bioequivalent to Shire’s product [[14/10/05f]].

The new patent relates to the release profile of the active ingredient in Adderall XR - the same profile that Shire is arguing should have to be demonstrated by copycat versions of the drug. In effect, the company is trying to place its generic rivals between a rock and a hard place: if the FDA accepts its petition and requires all generics to exhibit this profile, the companies will fall foul of the patent, according to a Reuters report.

Adderall XR brought in $205 million dollars in sales in the second quarter of this year, out of total company revenues of $425 million [[29/07/05f]]. Shire maintains that its US patents on the product provide protection out to 2018.

Shire has also been in negotiations with Barr about the possibility of allowing the generic company to launch a licensed generic ahead of the 2018 patent expiry [[19/08/05a]].