Dose-related effects of prostaglandin F2 alpha isopropylester on intraocular pressure, refraction, and pupil diameter in monkeys.

Topical application of Prostaglandin F2 alpha (PGF2 alpha) to the eye reduces intraocular pressure (IOP) in all mammalian species studied thus far, including humans. The L-isopropylester derivative is currently the one most commonly used in experimental and clinical studies. Dose-response relationships were determined between PGF2 alpha-IE and IOP, pupillary diameter, and refraction in ketamine-anesthetized ocular normotensive cynomolgus monkeys. Single doses of 10 and 30 micrograms had smaller and less consistent but longer lasting IOP-lowering effects than repeated doses (twice daily for 3 days) of 1-5 micrograms. For repeated dosing in this manner, the just-maximal dose is probably between 2-5 micrograms, producing a approximately 70% reduction in IOP to a final IOP of approximately 5 mm Hg. Continuing treatment for up to 18 days did not further enhance the efficacy of twice daily treatment with a submaximal 1-microgram dose. Partial reversal of anesthesia-induced tonic accommodation occurred with single 10- and 30-micrograms doses and with repeated 1-microgram doses, but additional myopia of 0.5-1.5 diopters was induced with repeated higher doses. These physiologic findings and previous morphologic data are consistent with a proposed dual PG action on the ciliary muscle, one involving a short-onset long-lasting direct effect on the muscle fibers (causing relaxation and narrowing of the muscle bundles) and the second involving a slowly developing but shorter duration dissolution of the intermuscular connective tissues.