BACKGROUND: Pulmonary arterial hypertension remains incurable and has previously required difficult parenteral therapy. Endothelin-1(ET-1) is an important mediator of pulmonary arterial hypertension. The recent availability of oral therapies, including endothelin receptor antagonists, has improved ease of use for patients, but most patients remain symptomatic to a significant degree. Two classes of ET-1 receptors have been described, ET(A) and ET(B). It has previously been unclear whether both receptors must be blocked in pulmonary arterial hypertension, or only the ET(A) receptor.
METHODS: The Sitaxsentan To Relieve ImpaireD Exercise-2 (STRIDE-2) study followed by STRIDE-2X exposed patients with pulmonary arterial hypertension to the highly selective ET(A) antagonist sitaxsentan (n = 145), or to bosentan (n = 84), a nonselective ET(A) and ET(B) antagonist. The total exposure duration and follow-up period was 1 year. Pre-specified comparisons included time to discontinuation of monotherapy, time to clinical worsening, incidence of elevated hepatic transaminase levels > 3 x upper limit of normal and survival.
RESULTS: Sitaxsentan therapy showed significant benefit over bosentan with respect to discontinuation of monotherapy at 1 year (24% vs. 43%, P = 0.002), clinical worsening at 1 year (28% vs. 39%, P = 0.0425), elevated hepatic transaminases at 1 year (4% vs. 14%, P = 0.014) and 1-year survival (96% vs. 88%, P = 0.028).
CONCLUSIONS: STRIDE-2 and its extension, STRIDE-2X, suggest significant benefit of sitaxsentan compared with bosentan, in terms of efficacy and reduced hepatotoxicity. The former may be related to the high ET(A) receptor selectivity of sitaxsentan.