SteadyMed Therapeutics (NASDAQ:STDY) said today it that the Patent Trial and Appeal Board of the U.S. Patent and Trademark Office initiated an inter partes review against a United Therapeutics patent.

The patent in question, No. 8,497,393, is related to a process to purify prostacyclin derivatives, such as treprostinil, which is used in United Therapeutics’ Remodulin and SteadyMed’s drug candidate Trevyent, designed to treat pulmonary arterial hypertension.

“The initiation of this IPR by PTAB is a significant decision in favor of SteadyMed. While we have an appreciation for the patent process in the U.S., we believe that the patent in question is invalid. We are pleased that the PTAB, by its action to institute the formal review process, appears to believe that there is sufficient doubt about the validity of certain claims of the ‘393 patent. We look forward to submitting our new drug application for Trevyent, which has been granted orphan designation, later this year. We are eager to see patients benefit from Trevyent, if approved, we have begun early preparation work for commercialization and believe that we will make significant in-roads to the PAH market,” CEO Jonathan Rigby said in a press release.

San Ramon, Calif.-based Steadymed said that IPR reports from 2012-2015 indicated that 74% of reviews were resolved by finding all claims unpatentable, cancelling claims and rendering patents invalid. Only 14% of cases were resolved by finding some claims unpatentable and cancelling those, and 12% were resolved by finding all claims patentable.

Last July, SteadyMed said it inked an exclusive deal with Cardiome for commercialization of its Treyvant product in regions outside the U.S., hinging on its regulatory approval in those regions.

Cardiome will have exclusive rights to the territories of the European Union, Canada and the Middle East, SteadyMed said.