SYSTEMIC ABSORPTION AND SYSTEMIC EFFECTS OF OCULARLY ADMINISTERED DEXMEDETOMIDINE IN RABBITS

Dexmedetomidine is a selective alpha2-adrenoceptor agonist which has p reviously been shown to reduce the ocular pressure of normotensive rab bits as well as those with pressures artificially elevated by laser ir radiation. In this study instillation of an equivalent hypotensive dos e (12.5 mug) did not cause changes in heart rate, blood pressure, bloo d glucose or plasma catecholamine content even though dexmedetomidine could be detected in plasma. However, this dose given intravenously (i .v.) was also without effect. Higher ocular doses resulted in equivale nt bradycardia and changes in blood glucose levels as when the dose wa s given i.v. These two parameters proved to be most sensitive indicato rs of systemic alpha2-agonism, blood pressure did not change and plasm a catecholamine levels were too low to be reliably assayed. It is conc luded that when hypotensive doses of dexmedetomidine are instilled int o the eye, intraocular concentrations are sufficiently high to exert p harmacological effects. As it is absorbed into the general circulation , it is diluted such that its systemic effects are minimal.