Brand Name: Alphagan
Generic: Brimonidine
Mechanism of Action: Brimonidine is a relatively selective alpha adrenergic receptor agonist that in radioligand binding assays and in functional assays, is approximately 1 000 times more selective for the alpha-2 adrenoceptor than the alpha-1 adrenoceptor. This selectivity results in the absence of vasoconstriction in microvessels associated with human retinal xenografts.
Topical administration of brimonidine decreases intraocular pressure (IOP) in humans. When used as directed, brimonidine ophthalmic solution reduces elevated IOP with minimal effect on cardiovascular parameters.
Brimonidine has a rapid onset of action, with the peak ocular hypotensive effect occurring at approximately 2 hours post-dosing. The duration of effect is 12 hours or greater.
Fluorophotometric studies in animals and humans suggest that brimonidine has a dual mechanism of action. Brimonidine lowers IOP by reducing aqueous humor production and increasing uveoscleral outflow.
Pharmacodynamics: Brimonidine has no effect on pulmonary function or exercise-induced tachycardia. The cardiovascular effects of brimonidine during exercise in normal volunteers were found to be limited to a slight suppression of systolic blood pressure, which was clinically insignificant, during the recovery period following a treadmill test.
After ocular administration of brimonidine 0.2% twice daily (both eyes) in humans for 10 days, plasma concentrations were low (mean Cmax=0.06 ng/mL). Plasma brimonidine levels peaked within 1 to 4 hours and declined with a systemic half-life of approximately 3 hours.
In humans, brimonidine is eliminated rapidly via extensive systemic metabolism; there is no marked systemic accumulation after multiple dosing. It is metabolized primarily by the liver. Urinary excretion is the major route of elimination of the drug and its metabolites. Approximately 87% of an orally-administered radioactive dose was eliminated within 120 hours, with 74% found in the urine in the first 96 hours.
Brimonidine ophthalmic solution 0.2% should be used with caution in patients with known hypersensitivity to other alpha-adrenoceptor agonists.
Although brimonidine had minimal effect on blood pressure and heart rate of patients in clinical studies, caution should be exercised in treating patients with severe cardiovascular disease.
Brimonidine has not been studied in patients with hepatic or renal impairment; caution should be exercised in treating such patients.
Brimonidine should be used with caution in patients with depression, cerebral or coronary insufficiency, Raynaud's phenomenon, orthostatic hypotension or thromboangiitis obliterans. prescription canada
|
