Shire Pharmaceuticals has agreed to pay up to $500 million dollars to New River Pharmaceuticals as part of a deal for the latter company’s Phase III ADHD drug candidate, NRP104.

Shire, which first announced the deal last month [[05/01/05h]], said that it would pay New River an initial $50 million signing fee, followed by a further $50 million if the US Food and Drug Administration agrees to review the drug. New River could also receive up to $300 million in milestone payments, as well as a $100 million bonus if certain sales targets are met. In the all-important US market, Shire will retain 75% of profits for the first two years following launch, with profits to be split equally thereafter.

The firms believe that NRP104 could offer advantages over currently available ADHD treatments, because it is inactive until metabolised in the gastrointestinal tract, which could reduce the risk of potential abuse or overdose. In addition, the firms have said that the drug could have an improved safety profile over traditional stimulants – potentially giving it a boost in an increasingly competitive marketplace, as well as heading off the prospect of sliding sales of Shire’s top-selling ADHD treatment, Adderall XR (amphetamine salts extended-release), when copycat versions hit the market as early as next year.