Encysive Pharmaceuticals Inc. said it filed a formal dispute resolution request with U.S. regulators to contest a third approvable letter the company received for its hypertension drug Thelin.

On June 15, the company had received a letter from the Food and Drug Administration stating that its clinical development program for Thelin did not demonstrate the effectiveness needed for approval, it said in a statement.

Formal dispute resolution is an FDA process where sponsors can challenge regulatory decisions by bringing the dispute to the attention of FDA supervisors. (Reporting by Aniruddha Basu in Bangalore)