: PRéCIS: Three randomized, multicenter studies demonstrated the stable intraocular pressure-lowering effects and tolerability of omidenepag isopropyl in patients with primary open-angle glaucoma and ocular hypertension; 0.002% was identified as the optimal dose for further investigation. PURPOSE: The purpose of this study was to assess the safety and efficacy of omidenepag isopropyl, a selective EP2 agonist, and to determine the optimal dose for further investigation. PATIENTS AND METHODS: Three randomized, controlled, masked, multicenter studies were conducted in United States (study 1, NCT01868126; study 2, NCT02179008) and Japan (study 3, NCT02623738). Patients were randomized to 1 of 7 omidenepag isopropyl concentrations (0.0003%, 0.001%, 0.0012%, 0.0016%, 0.002%, 0.0025%, and 0.003%), latanoprost (0.005%), or placebo, 1 drop once daily for 28 days (studies 1 and 3) or 90 days (study 2). Primary endpoints were the observed mean diurnal intraocular pressure (IOP) and IOP at each time point on the final visit (studies 1 and 2) and change from baseline in mean diurnal IOP at week 4 (study 3). RESULTS: IOP-lowering effects of omidenepag isopropyl 0.0003% to 0.002% increased dose-dependently. Omidenepag isopropyl 0.002% and 0.0025% resulted in clinically relevant mean diurnal IOP reductions from baseline that were similar to those of latanoprost and superior to placebo (P<0.005). Maximum reductions had already been achieved by week 1, and stable IOP-lowering effects were observed at all postbaseline time points up to 3 months. Most adverse events (AEs) were mild. Conjunctival hyperemia was the most frequently reported AE, the incidence of which increased dose-dependently. The safety profiles of omidenepag isopropyl 0.002% and 0.0025% were similar, with a slightly lower incidence of AEs in the 0.002% group. CONCLUSIONS: Omidenepag isopropyl demonstrated stable IOP-lowering effects and was well tolerated; 0.002% was identified as the optimal dose for phase 3 investigation.