Travoprost is the Alcon trade name for fluprostenol isopropyl ester, an F-series prostaglandin analog which has been approved for use as an ocular hypotensive drug. Fluprostenol isopropyl ester is a prodrug which is converted by esterase enzymatic activity in the cornea to yield the corresponding free acid. 5-trans Fluprostenol isopropyl ester (5-trans Travoprost) in an impurity that is routinely found in bulk preparations of fluprostenol isopropyl ester in amounts ranging from 1-3%. The pharmacology of 5-trans fluprostenol isopropyl ester has not been studied extensively to date.