Latanoprost is an F-series PG analog which has been approved for use as an ocular hypotensive drug. Latanoprost is an isopropyl ester, a prodrug form which is converted to latanoprost (free acid) by endogenous esterase enzymes. The free acid form is 200 times more potent than latanoprost as an FP receptor ligand for the human recombinant FP receptor. Latanoprost is the isopropyl ester of a PGF2α analog containing an aromatic group (17-phenyl) in the ω-chain. Lat-FA is the corresponding carboxylic acid of this analog. Lat-FA is a potent FP receptor agonist with an EC50 of 3.6 nM for human FP receptors, which is twice the potency of PGF2α. The efficacy of PG analog esters for the treatment of glaucoma correlates closely with the FP receptor binding affinity of the free acid. However, Lat-FA is more irritating and less effective than the prodrug latanoprost when applied directly to the eyes of human glaucoma patients.