Encysive Pharmaceuticals is refusing to give up on its blood pressure therapy Thelin in the USA, and has decided to conduct an additional Phase III trial of the drug in an attempt to finally get it onto the all-important US market.

In June, US regulators rejected Thelin (sitaxsentan sodium) for the treatment of pulmonary arterial blood pressure for the third time, on grounds that Encysive's development programme did not demonstrate the evidence of effectiveness needed for approval. The drug was given the green light for this indication by the European Medicines Agency in August last year.

At the time, the decision stunned the company’s chief executive Bruce Given, who insisted: “We believe we adequately addressed the issue raised by the FDA in the second approvable letter, and we are deeply disappointed in their decision”. He added that the firm “remains committed to Thelin in Europe, Australia and Canada, where it has been approved for sale,” but the FDA’s decision means that the company “may be required to make significant reductions in its infrastructure and workforce in the USA.”

Challenge dropped

Receipt of the third approvable letter prompted the firm to file a request for formal dispute resolution with the FDA over its decision, to which the agency replied that, while the data in the application are suggestive of the effectiveness of Thelin, there was not evidence of effectiveness needed for a green light, and again recommended an additional Phase III trial.

Encysive maintains that it had successfully addressed all of the questions raised by the FDA in its application, but says it decided that, after consulting with external experts, the best path forward for commercialising Thelin in the US would to conduct an additional Phase III study. Consequently, the group will not continue with its challenge to the FDA’s decision.

Further details regarding the trial, which has been crowned STRIDE 5, will be announced after the protocol has been finalised by the FDA.