Disclosed is a composition comprising an a prodrug of a prostanoid agonist of formula I, wherein the variables are defined in the specification, a carboxylic acid, sodium phosphate dibasic, sodium chloride, a solubilizing agent, and the remainder water, wherein the pH of the composition is adjusted from about 4 to 8. The present disclosure is based on the discovery that a marked increase in aqueous stability (and thereby shelf life) of prostanoid agonist prodrug compositions is achieved by incorporating into the compositions certain well-defined carboxylic acids, and thereafter adjusting the pH of the compositions from about 4.0 to about 8.0. As a result, the compositions and methods disclosed herein provide the aqueous stability required for marketable topical drug treatments of a wide variety of ocular disorders.
