Pfizer halts Phase III trial, withdraws Thelin

Pfizer ($PFE) announced that it is withdrawing pulmonary arterial hypertension drug Thelin (sitaxentan) after the company observed  life-threathening liver toxicity issues in subjects enrolled in a Phase III trial. "Given the availability of alternate treatments, Pfizer has concluded that the overall benefit of Thelin no longer outweighs the risk in the general population of PAH patients," the company explained in a statement. Thelin competes with Actelion's blockbuster drug Tracleer, which is approved in the U.S.

Pfizer acquired Thelin after its 2008 buyout of Encysive Pharmaceuticals. The drug was first submitted 2006, but the agency demanded another late-stage trial of the treatment to prove Thelin met efficacy standards. Encysive tried unsuccessfully to get the agency to change its mind without having to conduct another trial, but the FDA did not relent. However, a Phase III trial did get under way after Pfizer spent $195 million to acquire the company in 2008. Encysive was successful in gaining approval for Thelin in Europe, Australia and Canada. Pfizer's Phase III trial of the drug has been halted and the company is recommending that patients on the drug be switched to another treatment as soon as possible.

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