Detection of the free acid of bimatoprost in aqueous humor samples from human eyes treated with bimatoprost before cataract surgery.

Purpose To determine whether bimatoprost is hydrolyzed to its free acid after topical application in humans in vivo. Design Prospective, masked, and vehicle controlled. Participants Thirty-one eyes of 31 patients with cataracts. Methods Beginning 7 days before scheduled cataract surgery, one eye of each patient was treated with bimatoprost 0.03% or vehicle once daily, with the last drop administered 2 to 12 hours before anterior chamber paracentesis before cataract surgery. In a masked fashion, aqueous humor specimens were assayed for bimatoprost and its free acid by high-pressure liquid chromatography and mass spectrometry. Main outcome measure Detection of the free acid of bimatoprost in aqueous humor. Results Aqueous humor concentrations of the free acid of bimatoprost were 22.0±7.0 nmol/l (mean ± standard error of the mean, n = 12) and 7.0±4.6 nmol/l (n = 8) at 2 and 12 hours, respectively, and below the limit of detection after vehicle (n = 10). Concentrations of bimatoprost (amide) were 5.7±1.4 and 1.1±0.4 nmol/l at 2 and 12 hours, respectively, and undetectable after vehicle. Conclusion After topical application of bimatoprost in humans, a sufficient concentration of its free acid, a potent FPprostanoid receptor agonist, is found in the aqueous humor to account for its ability to reduce intraocular pressure.