Novartis' generics arm Sandoz has filed a copycat version of Shire's attention-deficit hyperactivity disorder drug Vyvanse with regulators in the US.

The company has submitted an Abbreviated New Drug Application for a generic version of all strengths of Vyvanse (lisdexamfetamine dimesylate) with the US Food and Drug Administration. 

Shire noted that this is the first challenge to Vyvanse in the US, and that it relates to all 16 patents listed in the FDA's Orange Book, which aren't due to expire until 2023.

In March last year a US court upheld an FDA decision in 2007 to grant Shire five-year new chemical entity market exclusivity for Vyvanse, following Icelandic firm Actavis' attempt to overturn it.

Because of the court decision, no generic versions of the drug can be submitted to the FDA until Febraury 2012, or until February 2011 should a generic applicant challenge the US patents covering Vyvanse.

Shire has 45 days (from the receipt of the letter) to decide whether it will fight back with a patent infringement suit.

Vyvanse pulled in sales of £634 million for the group last year.