Iloprost is a drug used to treat pulmonary arterial hypertension (PAH), scleroderma, Raynaud's phenomenon and other diseases in which the blood vessels are constricted and blood can't flow to the tissues. This damages the tissues and causes high blood pressure. Iloprost works by opening (dilating) the blood vessels to allow the blood to flow through again. It was developed by the pharmaceutical company Schering AG and is marketed by Bayer Schering Pharma AG in Europe and Actelion Pharmaceuticals in the USA. Iloprost is a drug used to treat pulmonary arterial hypertension (PAH), scleroderma, Raynaud's phenomenon and other diseases in which the blood vessels are constricted and blood can't flow to the tissues. This damages the tissues and causes high blood pressure. Iloprost works by opening (dilating) the blood vessels to allow the blood to flow through again. It was developed by the pharmaceutical company Schering AG and is marketed by Bayer Schering Pharma AG in Europe and Actelion Pharmaceuticals in the USA. Iloprost is a synthetic analogue of prostacyclin PGI2. Iloprost dilates systemic and pulmonary arterial vascular beds. It also affects platelet aggregation but the relevance of this effect to the treatment of pulmonary hypertension is unknown. The two diastereoisomers of iloprost differ in their potency in dilating blood vessels, with the 4S isomer substantially more potent than the 4R isomer. While Iloprost is an analog of PGI2 that activates PGI2's receptor, the Prostacyclin receptor, to stimulate vasodilation, it has little selectivity in that it binds to and activates all four receptors for prostaglandin E2 viz., Prostaglandin EP1 receptor, Prostaglandin EP2 receptor, Prostaglandin EP3 receptor, and Prostaglandin EP4 receptor. Activation of the EP2 and EP4 receptors cause vasodilation but activation of the EP3 receptor causes vasoconstriction.