[2] Sitaxentan is a small molecule that blocks the action of endothelin (ET) on the endothelin-A (ETA) receptor selectively (by a factor of 6000 compared with the ETB).

[3] It is a sulfonamide class endothelin receptor antagonist (ERA) and is undergoing Food and Drug Administration (FDA) review for treating pulmonary hypertension.

The rationale for benefit compared with bosentan, a nonselective ET blocker, is negligible inhibition of the beneficial effects of ETB stimulation, such as nitric oxide production and clearance of ET from circulation.

In July 2006, sitaxentan received a second approvable letter stating that efficacy outcome issues raised in the context of the STRIDE-2 study were still unresolved.

In September 2007 the company announced that it was making preparations for another phase III clinical trial (intended to be named STRIDE-5) to overcome the FDA's concerns.