Timolol and Epinephrine: A Clinical Study of Ocular Interactions

In a crossover design study, we assessed effects on intraocular pressure, pupillary diameter, pulse rate, and blood pressure over six hours of one drop of 0.5% timolol maleate and 2% epinephrine hydrochloride in one eye. Both eyes of each patient had been pretreated for one week with twice-daily applications of epinephrine or timolol, respectively. In random sequence, 20 patients (40 eyes) participated in both phases of the study. Pretreatment with timolol significantly reduced the ocular hypotensive effect of epinephrine (from 15.3% to 4.6%); epinephrine pretreatment did not affect the pressure reduction of timolol. Pretreatment with timolol enhanced the mydriatic effect of epinephrine (from 35.8% to 71.9% pupillary dilation); pretreatment with epinephrine resulted in an apparent mydriatic effect for timolol.