Background and Purpose—Clazosentan, an endothelin receptor antagonist, has been shown to reduce vasospasm after aneurysmal subarachnoid hemorrhage (aSAH). CONSCIOUS-3 assessed whether clazosentan reduced vasospasmrelated morbidity and all-cause mortality postaSAH secured by endovascular coiling. Methods—This double-blind, placebo-controlled, phase III trial randomized patients with aSAH secured by endovascular coiling to
14 days intravenous clazosentan (5 or 15 mg/h) or placebo. The primary composite end point (all-cause mortality; vasospasm-related new cerebral infarcts or delayed ischemic neurological deficits; rescue therapy for vasospasm) was evaluated 6 weeks postaSAH. The main secondary end point was dichotomized extended Glasgow Outcome Scale (week 12). Results—CONSCIOUS-3 was halted prematurely following completion of CONSCIOUS-2; 577/1500 of planned patients (38%) were enrolled and 571 were treated (placebo, n
189; clazosentan 5 mg/h, n
194; clazosentan 15 mg/h, n
188). The primary end point occurred in 50/189 of placebo-treated patients (27%), compared with 47/194 patients (24%) treated with clazosentan 5 mg/h (odds ratio [OR], 0.786; 95% CI, 0.479–1.289; P
0.340), and 28/188 patients (15%) treated with clazosentan 15 mg/h (OR, 0.474; 95% CI, 0.275–0.818; P
0.007). Poor outcome (extended Glasgow Outcome Scale score
4) occurred in 24% of patients with placebo, 25% of patients with clazosentan 5 mg/h (OR, 0.918; 95% CI, 0.546–1.544; P
0.748), and 28% of patients with clazosentan 15 mg/h (OR, 1.337; 95% CI, 0.802–2.227; P
0.266). Pulmonary complications, anemia, and hypotension were more common in patients who received clazosentan than in those who received placebo. At week 12, mortality was 6%, 4%, and 6% with placebo, clazosentan 5 mg/h, and clazosentan 15 mg/h, respectively. Conclusions—Clazosentan 15 mg/h significantly reduced postaSAH vasospasm-related morbidity/all-cause mortality; however, neither dose improved outcome (extended Glasgow Outcome Scale). Clinical Trial Registration—URL: http://clinicaltrials.gov. Unique identifier: NCT00940095. (Stroke. 2012;43:1463-1469.)