Brimonidine tartrate is an imidazolin derivative that is a selective agonist of α2-adrenoceptors. As it binds less to α1-adrenoceptor, the side effects it mediates decrease. It acts sympathomimetic. Due to the lower chamber water formation and the increased uveoscleral outflow, the intraocular pressure decreases in the open-angle glaucoma (reserve drug). It can also be used to treat facial erythema, as it leads to the constriction of blood vessels in the facial area.