Sitaxsentan treatment for patients with pulmonary arterial hypertension discontinuing bosentan

Bosentan, an oral ET(A)/ET(B) receptor antagonist, is approved for the treatment of pulmonary arterial hypertension (PAH). However, some patients discontinue bosentan because of hepatotoxicity or inadequate efficacy. Sitaxsentan, an oral, ET(A)-selective endothelin antagonist currently under investigation, may be an alternative treatment option. In this study we evaluate the safety and efficacy of sitaxsentan in patients discontinuing bosentan.

Forty-eight patients with idiopathic PAH or PAH associated with connective-tissue disease or congenital heart disease were randomized (double-blind) to a single daily dose of either 50 mg or 100 mg sitaxsentan. Thirty-five of the 48 patients discontinued bosentan because of inadequate efficacy, as judged by the investigator, and 13 discontinued bosentan for safety concerns. Study end-points included change in 6-minute walk distance (6MWD), change in World Health Organization (WHO) functional class, time to clinical worsening, and change in Borg dyspnea score (Borg) from baseline to Week 12.

With 100 mg sitaxsentan, 5 of 15 patients (33%) who discontinued bosentan because inadequate efficacy improved, demonstrating a >15% increase in 6MWD, vs 2 of 20 patients (10%) treated with 50 mg sitaxsentan. Fifteen percent and 20% of these patients had a >15% decrease in 6MWD in the 50- and 100-mg groups, respectively. Similar results were seen for the Borg and WHO functional class. Of the 12 patients discontinuing bosentan because of hepatotoxicity, 1 developed elevated liver enzymes at 13 weeks of sitaxsentan therapy. Overall, sitaxsentan was well tolerated.

Sitaxsentan may represent a safe and efficacious alternative endothelin receptor antagonist for patients discontinuing bosentan.