Shire Pharmaceuticals has received another setback in its bid to get US approval for its new attention deficit hyperactivity disorder drug, which has been developed with US partner New River Pharmaceuticals.

The company noted that the US Food and Drug Administration has issued a second approvable letter for Vyvanse (lisdexamfetamine dimesylate), formerly known as NRP104, requesting more data. The first such letter was received in October and at the time, Shire said that the agency’s notice was not unexpected as it often requires new drugs for ADHD to be assessed by the US Drug Enforcement Agency to determine the restrictions and monitoring that should be put in place on distribution.

With the second letter, Shire claimed that "the data requested are routine" and no additional studies have been requested. The company added that this latest development should not delay a launch of Vyvanse in the second quarter.

Shire's shares slipped slightly on the news, as did New River's stock, amid fears that the superiority claims made for Vyvanse, over its predecessor, the firm's top-selling ADHD treatment Adderall XR, are still an issue. Adderall loses patent protection in 2009 and Shire has previously stated that the new drug will have potential sales of more than $1 billion annually.