Preclinical safety profile of brimonidine

Brimonidine is a selective alpha 2-adrenergic agonist developed for lowering intraocular pressure in glaucoma patients. Since brimonidine will be used in long-term theraphy, the safety of this drug is an important feature for its clinical success. Brimonidine has been evaluated in a number of safety studies using doses much greater than those in humans. In this paper chronic and carcinogenicity studies are presented. The results of the 6-month ocular/systemic study in rabbits and the 1-year ocular/systemic study in monkeys with 0.2, 0.5, and 0.8% brimonidine ophthalmic formulations showed no ocular or organ toxicity. The highest concentration of 0.8% used in rabbits and monkeys resulted in plasma drug concentrations of 95 (Cmax) and 10 (C2hr) times, respectively, higher than those seen in humans following topical dosing. Dose-related transient exaggerated pharmacologic effects of sedation were observed in the 1-year oral study in monkeys without any organ toxicity. The dose that elicited an apparent pharmacologic effect produced a plasma drug concentration that was approximately 115 times higher than that in humans. In 2-year carcinogenicity studies in mice and rats using doses that produced plasma concentrations 77 and 118 times, respectively, higher than those seen in humans, no oncogenic effect was observed. Based on the extensive safety research on brimonidine, it was concluded that this drug has an excellent safety profile.