Cloprostenol is a synthetic PGF2α analog and a potent FP receptor agonist. (+)-15-epi Cloprostenol is the 15(S), or 15β-hydroxy enantiomer of (+)-cloprostenol. This epimer is less active by several orders of magnitude as an FP receptor ligand when compared to 15(R)-cloprostenol. However, the specific activity of this isomer has not been well studied.