Clazosentan (INN, brand name Pivlaz[1]) is a drug belonging to the class of endothelin receptor antagonists.

The endothelin 1 receptor is one of the strongest known vasoconstrictors.

After subarachnoidal bleedings, irritation of the blood vessels can lead to a vasospasm and thus to an ischaemia, an insufficient blood supply to brain tissue.

One possible effect of this is, in turn, an ischaemic stroke.

In a randomized trial with patients who had aneurysmal subarachnoid bleeding and were being treated with endovascular coiling, 15 mg/h clazosentan significantly reduced vasospasm-related morbidity and all-cause mortality.