The purpose of this study is to evaluate the safety and potential therapeutic benefit of use of clazosentan in reversing cerebral vasospasm (a narrowing of blood vessels in the brain due to the presence of blood in the space around the brain) in patients who have suffered a condition known as aneurysmal subarachnoid hemorrhage caused by bleeding onto the surface of the brain from a ruptured brain aneurysm

Aneurysmal subarachnoid hemorrhage (aSAH) is characterized by bleeding onto the brain surface due to a rupture of a pouch or bulge in a brain vessel (called an aneurysm). It is a rare but serious condition with a high risk of death. Even patients who have had successful repair of the aneurysm remain at risk for developing cerebral vasospasm, which can result in harmful conditions related to the lack of oxygen to parts of the brain and death. Cerebral vasospasm usually occurs within the first couple of weeks after aSAH, and it is difficult to treat. Currently there is no safe, efficacious and widely available treatment. Previous animal studies have shown that a new drug under investigation, clazosentan, was able to reverse cerebral vasospasm in animal models of SAH. A first trial conducted in a small number of patients showed some benefit of clazosentan in reversing established cerebral vasospasm after aSAH. Clazosentan has already been evaluated in the prevention of cerebral vasospasm in several large clinical trials in aSAH. This current study aims to evaluate if clazosentan is effective and safe in the treatment of cerebral vasospasm after aSAH.

Inclusion Criteria:

• Signed informed consent from the subject or proxy/legal representative
• Aneurysmal subarachnoid hemorrhage (aSAH)confirmed by digital subtraction angiogram (DSA) or computed tomography angiogram (CTA), successfully secured by surgical clipping or endovascular coiling within 72 hours of rupture
• World Federation of Neurological Surgeons (WFNS) grade 1-4 at admission, and which must not increase to grade 5 at the time of enrollment
• Moderate or severe global cerebral vasospasm at the time of enrollment, documented by digital subtraction angiography (DSA) performed not earlier than 48 hours post aneurysm-securing procedure
• Women of childbearing potential must have a negative serum pregnancy test at screening and must use a reliable method of contraception from hospital discharge up to 30 days after discontinuation of study drug infusion, and fertile males must use a condom as a contraceptive method during this same period

Exclusion Criteria:

• SAH due to causes other than a saccular aneurysm
• Any moderate or severe cerebral vasospasm on angiography prior to the aneurysm-securing procedure
• Presence of a new or worsened cerebral infarct or evidence of significant bleeding post aneurysm-securing procedure, or re-bleeding, on a CT scan performed within 24 hours prior to enrollment
• Total bilirubin > 2 times the upper limit of normal, and / or a known diagnosis or clinical suspicion of liver cirrhosis or moderate to severe hepatic impairment
• Any severe or unstable concomitant condition or disease (e.g., cancer, hematological, or coronary disease) or chronic condition (e.g., drug abuse, severe alcoholism), which, in the opinion of the investigator, would interfere with the assessment of the safety or effect of the study treatment