Ocular hypotensive efficacy of topical epinephrine in normotensive and hypertensive rabbits: continuous drug delivery vs eyedrops.

The ocular hypotensive efficacy of continuously delivered epinephrine is compared to that of pulsed doses provided by eyedrops in both normotensive and hypertensive rabbit eyes. In normotensive eyes, 2 microgram/hr and 4 microgram/hr epinephrine delivered into the tear film continuously for 12 hours reduces intraocular pressure as well as eyedrop pulses of 0.5% epinephrine hydrochloride or 2% epinephrine bitartrate (doses of 500 and 1100 microgram, respectively). Ocular hypertension induced by an intragastric water load in rabbits is significantly inhibited by continuous delivery of epinephrine at the rates of 3 or 6 microgram/hr, or by 2% epinephrine bitartrate (1% free base) eyedrops. Epinephrine delivered continuously at rates of 2-6 microgram/hr for 6 to 12 hours (12-72 microgram total) has hypotensive efficacy equivalent to 15 to 40 times as much epinephrine applied once in eyedrops. Epinephrine bitartrate eyedrops reduce tear film pH well below normal. Continuous delivery of epinephrine bitartrate does not reduce tear film pH below normal levels.