Encysive Pharmaceuticals will conduct an additional Phase III trial for Thelin (sitaxsentan sodium) in pulmonary arterial hypertension rather than pursuing a formal dispute resolution with FDA on the product's "approvable" letters, the firm announced Sept. 24.

The study would likely take "years instead of months" because PAH is an orphan indication, Encysive CEO George Cole told "The Pink Sheet" DAILY earlier this month (¹ Also see "Encysive Dispute Resolution Request For Thelin Negged By FDA" - Pink Sheet, 6 September, 2007.).

FDA has sent three approvable letters to the firm regarding its NDA for sitaxsentan in PAH. The agency said Encysive did not demonstrate the evidence of effectiveness needed for approval even though it provided some evidence that the compound improves exercise tolerance in PAH (² Also see "Thelin's Third "Approvable" Letter Recommends Additional Clinical Trial" - Pink Sheet, 15 June, 2007.).

The company said it is moving forward to work with FDA to finalize the protocol for the new trial, to be called STRIDE 5.

"Encysive believes it had successfully addressed all of the questions" raised by FDA with regard to the Thelin NDA; however, after consulting with external experts, it decided that the best path forward for commercializing Thelin in the U.S. is to conduct an additional Phase III study, the firm said.

Gilead received FDA approval for its same-class endothelin receptor antagonist Letairis (ambrisentan) on June 15, the same day Encysive's third approvable letter, asking for an additional Phase III trial, was received by the Houston, Texas, firm.

Thelin has been approved for sale in Australia, Europe and Canada.

At the UBS Global Life Sciences Conference in New York Sept. 24, Cole said the firm expects to have 35 sales reps when Thelin is fully launched in the "Big 5" ex-U.S. countries - Canada, France, Germany, Italy and the U.K. Next year will be the first full year of sales for Thelin in those countries.

Cole also gave credit to Actelion for opening up the PAH market in Europe with Tracleer (bosentan). Tracleer's sales are expected to total $800 million to $900 million this year and growth is estimated at 30 percent per year, he said. "The patients are getting recognized earlier and they're getting on drug."

-Pamela Taulbee (p.taulbee@elsevier.com)

Encysive Rules Out FDA Dispute Resolution Path For Thelin NDA

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