24th Aug 2011, 11:41 am by Olivia D'Orazio

United Therapeutics (NASDAQ:UTHR) announced Wednesday that its drug intended to treat patients suffering from pulmonary arterial hypertension (PAH) failed to meet the primary goal of a phase three study, causing its stock to plummet.

PAH is a disease characterized by increased blood pressure in the lungs, and is marked by a reduced tolerance for exercise. Common symptoms include dyspnea, fatigue, and fainting, among others.

The endpoint of the 16 week placebo-controlled study was based on patients’ six-minute walk distance – a test designed to determine how far a patient can walk in six minutes, and factors in conditions such as fatigue, dyspnea, or shortness of breath.

Mean walk distance was 333 metres at the start of the study, and by the end of the trial, the mean change was ten metres, for those in the United drug arm and the placebo group.

There was not enough of a difference between patients treated with United’s drug, and with the placebo, to determine definitive results, the company said.

United’s treprostinil diethanolamine drug is a sustained-release treatment and is administered orally to treat PAH by inducing the widening of arteries in the lungs and body.

The trial, a randomized, double-blind, placebo-controlled study, examined 310 patients currently treated for the disease. Each patient received either the treprostinil diethanolamine drug, or a placebo, twice daily.

“While we did not achieve a statistically significant result for this trial, we believe the positive results from our previously-announced FREEDOM-M study support an NDA filing of oral treprostinil in treatment naive patients,” said president and CEO, Roger Jeffs.

Indeed, the company’s previous phase 3 trial, called Freedom-M, showed that the mean change for the six-minute walk distance for those taking United’s drug was 23 metres.

“Given that treprostinil is already approved for use in PAH by subcutaneous, intravenous and inhaled routes of administration, we believe the data obtained from all FREEDOM trials support an NDA for oral treprostinil in this indication,” added Jeffs.

United said it is continuing further review and analysis of the preliminary results from the latest trial. the company still also plans to complete the new Drug Application (NDA) for the drug, to be filed in the first half of 2012.

The Silver Spring, Maryland-based company’s stock on the Nasdaq exchange plunged 17.45% as of 10:59 am EDT, to trade at $40.25 per share on Wednesday.