TOKYO, Aug 11 (Reuters) - Japan's Astellas Pharma Inc said on Tuesday it would challenge the U.S. Food and Drug Administration in court, after the regulator knocked back its request for higher hurdles for generic rivals to its mainstay transplant drug.
Its shares slid 5 percent.
Astellas lost U.S. patent protection for Prograf, a drug used to prevent organ rejection, in April 2008 although generic versions have yet to hit the market. Analysts have said generic competition is expected to be slower for Prograf than other drugs due to the risk of organ rejection.
The move comes as Japan's second-largest drugmaker has suffered development setbacks and faces the expiry of the U.S. patent for its Flomax urinary drug, another key drug for the company, in October.
Astellas said in a statement the FDA had substantially denied its request that generic versions require clinical trials to compare their absorption versus Prograf.
It also said it will request labelling changes that require doctors to be notified if a pharmacist is considering substituting a generic drug for Prograf.
Astellas' request took the form of a citizen petition. The FDA receives some 200 such petitions a year. The complaint will be filed in the U.S. District Court in Washington, D.C.
It shares dropped to 3,670 yen, underperforming the broader pharmaceutical sector which fell 0.5 percent. (Reporting by Yumiko Nishitani; Editing by Edwina Gibbs)