(+)-15(R)-Fluprostenol isopropyl ester is a prodrug (Travoprost) which is converted by esterase enzymatic activity in the cornea to yield the corresponding free acid. The free acid, (+)-15(R)-fluprostenol, is a potent FP receptor agonist. The 15(R)-epimers of most PGs are about 100 times less potent than the natural, 15(S)-isomers. However, the neighboring phenoxy group at C-16 reverses the absolute configuration at C-15 in the fluprostenol series; hence, 15(S)-fluprostenol is less active as an FP agonist than 15(R)-fluprostenol. The biology of 15(S)-fluprostenol has not been widely studied.