Potent and selective thromboxane A2/prostaglandin endoperoxide receptor antagonist (IC50 = 5.5 nM). Inhibits U-44069-induced contractions of guinea pig trachea (pA2 = 9.0) and human platelet aggregation in vitro (IC50 = 6.5 nM). Also prevents thromboxane-mediated endothelial cell death. Orally active in vivo.