Sitaxsentan treatment for patients with pulmonary arterial hypertension discontinuing bosentan

Background: Bosentan, an oral ETA/ETB 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, ETA-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. Methods: 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. Results: 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, I developed elevated liver enzymes at 13 weeks of sitaxsentan therapy. Overall, sitaxsentan was well tolerated. Conclusions: Sitaxsentan may represent a safe and efficacious alternative endothelin receptor antagonist for patients discontinuing bosentan.