20-ethyl Prostaglandin F2α (20-ethyl PGF2α) is an analog of PGF2α in which the ω-chain has been extended by the addition of two more methylene carbon atoms. It is therefore a modified version of the clinically approved glaucoma medication unoprostone.¹ Unoprostone also contains lower side chain modifications (13,14-dihydro-15-keto) which severely limit its affinity for FP receptors, contributing to its lack of potency as a medication. 20-ethyl PGF2α retains the natural 15(S) allylic hydroxyl in the lower side chain, which may improve its potency as an intraocular hypotensive agent compared to unoprostone. The 2 carbon extension in 20-ethyl-PGF2α increases the Ki (120 nM) for the FP receptor from bovine corpus luteum only about 2.5-fold compared to PGF2α (50 nM).² In vivo effects may be prolonged using 20-ethyl PGF2α, as the activity of 15-hydroxy PGDH using 20-ethyl PGF2α as a substrate is only 35% of the activity observed with PGF2α.^3,2