United Therapeutics Corporation announced today that the U.S. Food and Drug Administration (FDA) has acknowledged the resubmission of the new drug application (NDA) for treprostinil diolamine extended release tablets (oral treprostinil) for the treatment of pulmonary arterial hypertension. The FDA classified the resubmission as a complete, class 1 response to FDA's October 23, 2012 complete response letter and the FDA set a user fee goal date of March 31, 2013.