Which of the following medications is an alpha-2 adrenergic agonist used in glaucoma?

Brimonidine is an alpha-2 adrenergic agonist that is specifically indicated for the treatment of glaucoma. It works by reducing aqueous humor production and increasing uveoscleral outflow, which helps to lower intraocular pressure (IOP) in patients with glaucoma. By stimulating alpha-2 receptors, brimonidine decreases sympathetic outflow, further contributing to its therapeutic effects.

Timolol is a nonselective beta-blocker, commonly used in glaucoma management, but it does not belong to the alpha-2 adrenergic agonist class. Acetazolamide is a carbonic anhydrase inhibitor that reduces the production of aqueous humor but is not an alpha-2 agonist. Pilocarpine is a cholinergic agent that increases the outflow of aqueous humor by inducing miosis, but again, it is not classified as an alpha-2 adrenergic agonist. Thus, brimonidine is correctly identified as the medication that fits the classification and usage pertinent to glaucoma management.