On the use of ketamine in ocular pharmacological studies

The effects of ketamine anesthesia in ocular pharmacological studies were investigated in albino rabbits over a period of 6 hr. Ketamine injection (30 or 90 mg/kg, i.m.) was accompanied by a 6 mm Hg elevation of intraocular pressure (IOP), lasting for 2-4 hr. Body temperature (Tb) showed an initial significant increase followed by a decrease, with changes ranging between +1.6 to -1.2 degrees C. Aqueous humor levels of ethoxzolamide following topical application of a 2% suspension were 2-9 times higher in ketamine-treated rabbits. The observed elimination rate constant for ethoxzolamide was A = -0.34 hr-1 in ketamine-treated rabbits, half of that observed in normal rabbits (A = -0.73 hr-1). In spite of the higher ethoxzolamide levels in aqueous humor, the measured ocular hypotensive response to ethoxzolamide was greatly reduced by ketamine treatment. These findings demonstrate that great care should be taken in interpretation and comparison of ocular pharmacological data obtained in ketamine-anesthetized rabbits.