title: Distribution of brimonidine into anterior and posterior tissues of monkey, rabbit, and rat eyes.
abstract: The objectives of the study were to evaluate the distribution of brimonidine (alpha2-adrenergic agonist) into anterior and posterior ocular tissues. Single or multiple doses of a 0.2 or 0.5% brimonidine tartrate solution were administered to one or both eyes of monkeys or to one eye of rabbits. Brimonidine was administered intraperitoneally to rats. After topical administration, [14C]brimonidine was rapidly absorbed into the cornea and conjunctiva and distributed throughout the eye. [14C]Radioactivity was higher and cleared more slowly in pigmented tissues (iris/ciliary body, choroid/retina, and optic nerve) than in nonpigmented tissues. Single and multiple dosing led to a similar drug distribution, with higher levels of brimonidine measured in pigmented tissues after multiple dosing. Most of the radioactivity extracted from ocular tissues represented unchanged brimonidine. In the rabbits and the monkey treated in only one eye, levels of radioactivity in the untreated eye were low, consistent with the low systemic levels and rapid drug clearance. Posterior ocular tissue concentrations of radioactivity exceeded systemic blood concentrations. The vitreous humor brimonidine concentrations in monkeys treated topically with 0.2% brimonidine tartrate was 82 +/- 45 nM. Vitreous levels in rabbits confirmed the penetration of brimonidine to the posterior segment. Similar concentrations of brimonidine (22 to 390 nM) were measured in the vitreous and retina of rats injected intraperitoneally with brimonidine. Both topically applied and systemically administered brimonidine reach the back of the eye at nanomolar concentrations sufficient to activate alpha2-adrenergic receptors. The brimonidine levels achieved at the retina are relevant for neuroprotection models.
authors.affiliation: Allergan, Inc., Irvine, California 42623-9534, USA. Acheampong_Andrew@allergan.com
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Acheampong
authors.forename: Martha
authors.initials: M
authors.lastname: Shackleton
authors.forename: Brian
authors.initials: B
authors.lastname: John
authors.forename: James
authors.initials: J
authors.lastname: Burke
authors.forename: Larry
authors.initials: L
authors.lastname: Wheeler
authors.forename: Diane
authors.initials: D
authors.lastname: Tang-Liu
mesh_terms: D000287:Administration, Topical; D000818:Animals; D000068438:Brimonidine Tartrate; D002250:Carbon Radioisotopes; D002851:Chromatography, High Pressure Liquid; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D005123:Eye / Q000737:chemistry / Q000378:metabolism*; D007274:Injections, Intraperitoneal; D007498:Iris / Q000737:chemistry / Q000378:metabolism; D008252:Macaca fascicularis; D008657:Metabolic Clearance Rate; D011810:Quinoxalines / Q000008:administration & dosage / Q000493:pharmacokinetics*; D011817:Rabbits; D051381:Rats; D014018:Tissue Distribution; D014822:Vitreous Body / Q000737:chemistry / Q000378:metabolism
chemical_list: D002250:Carbon Radioisotopes; D011810:Quinoxalines; D000068438:Brimonidine Tartrate