Elevated intraocular pressure (IOP) is an important risk factor in developing glaucoma. Certain prostaglandins such as PGF2α and PGD2, have been shown to reduce IOP. AL 6598 is the isopropyl ester prodrug of AL 6556, a PGD2 receptor agonist that binds to DP receptors with a Ki value of 3.2 µM and demonstrates an EC50 value of 0.80 µM in an in vitro functional assay. Designed to enhance corneal absorption, AL 6598 produces a maximum 53% drop in IOP of the ocular hypertensive monkey with a 1 µg dose given twice daily.