Sitaxentan for the Oral Treatment of Pulmonary Arterial Hypertension: Benefits from Endothelin Receptor Subtype Selectivity?

Pulmonary arterial hypertension (PAH) is a deadly and underdiagnosed disease which causes right heart failure secondary to pressure overload resulting from the thickening of the pulmonary artery endothelium, associated with elevated levels of circulating endothelin-1. Sitaxentan was the first endothelin antagonist with high selectivity for receptor subtype A (over subtype ET-B) to gain regulatory approval for the treatment of PAH in major pharmaceutical markets. This review traces the development history of sitaxentan, summarizes the designs and results from its clinical studies, and relates the drug's profile to that of the two other broadly available endothelin receptor antagonists, bosentan and ambrisentan. All three drugs have comparable therapeutic efficacy in the 6-minute walk test–-a frequently employed standard–-during the first 3-4 months of therapy. Their performance might differ slightly in other clinically relevant outcome measures, especially in longer-term treatment where fully comparable data have not yet been reported. In clinical trials of up to one year duration the propensity of sitaxentan to induce elevation of liver transaminases and hepatic failure was significantly lower than that of bosentan. As a once-daily oral drug with good tolerability sitaxentan has become a crucial element in the treatment of PAH.