Ralinepag is a cyclohexyl amide derivative patented by Arena Pharmaceuticals, Inc. as agonists of the human prostacyclin (PGI2) receptor useful for the treatment of pulmonary arterial hypertension. Ralinepag shows selectivity in both binding and functional assays with respect to most members of the prostanoid receptor family and a more modest 30-50-fold selectivity over the EP3 receptor. Ralinepag had an excellent PK profile across species. Enterohepatic recirculation most probably contributes to a concentration-time profile after oral administration in the cynomolgus monkey that showed a very low peak-to-trough ratio. Phase III clinical trial is currently ongoing.