Review: systemic absorption of topically applied ocular drugs in humans.

Literature on human plasma concentrations after instillation of ocular timolol, levobunolol, atropine, cyclopentolate, scopolamine, phenylephrine, betamethasone and technetium Tc 99m and theories of lacrimal drainage were reviewed. In all studies the eyedrops absorbed rapidly into the systemic circulation. Like the kinetics of the tracer substances in lacrimal scintigraphy, the plasma drug levels showed interindividual variations. Plasma levels of ocular drugs were lower when punctal occlusion was applied, the mechanism, however, could not be explained. Since an early and a late plasma peak was occasionally registered in some subjects in timolol and cyclopentolate studies, it is suggested that systemic absorption of ocular drugs is low during the nasolacrimal passage but occurs during conjunctival and nasal contact.