Bimatoprost (free acid) is a metabolically stable analog of prostaglandin F2a (PGF2a) and a potent agonist for the FP receptor. It binds to the FP receptor on ovine luteal cells with a relative potency of 756% compared to that of PGF2a.{2058} At the rat recombinant FP receptor expressed in CHO cells bimatoprost inhibits PGF2a binding with a Ki of 1.1 nM.{1374} The isopropyl ester of bimatoprost is slightly better than PGF2a isopropyl ester in reducing the intraocular pressure in the cat eye without any irritation.{1107} 8-iso-17-phenyl PGF2B is an isomer of bimatoprost that is epimerized at the 8 and 9 positions. There are no published reports on the biological activity of 8-iso-17-phenyl PGF2B.