Medical Health Encyclopedia

Adrenergic agonists activate muscles in the eye that dilate pupils and, therefore, increase outflow of aqueous fluid. Newer variations called alpha 2-adrenergic agonists reduce production of aqueous humor and also increase outflow through the uveoscleral pathway (the alternative channel to the trabecular meshwork). Older adrenergic agonists include epinephrine.

Alpha 2-Adrenergic Agonists. Apraclonidine (Iopidine) and brimonidine (Alphagan) are alpha 2-adrenergic agonists. These have generally been used before glaucoma surgery, but a number of studies are indicating that they may even be useful as primary therapy when used in combination with beta-blockers or other standard drugs.

Brimonidine is proving to be particularly effective for long-term therapy. (Apraclonidine is used for the short term.) It also may have nerve-protecting properties and may be safer than other drugs during pregnancy and for patients with asthma.Studies are finding that brimonidine was as effective and resulted in a better quality of life than the newer beta-blocker betaxolol. Comparison studies indicate that the combination of brimonidine and latanoprost is superior to timolol/dorzolamide (Cosopt) in lowering IOP.

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The most common side effects of brimonidine and apraclonidine are dry mouth and altered taste. They also commonly trigger an allergic reaction that causes red and itching eyes and lids, a major drawback. Brimonidine causes less of an allergic response than apraclonidine. Unlike apraclonidine, however, it can cause lethargy and mild low blood pressure. It also appears to remain effective longer.

Miotics (Pilocarpine and Others)

Miotics, also called cholinergic agonists, narrow the iris muscles and constrict the pupil. This action pulls the iris away from the trabecular meshwork and allows the aqueous humor to flow out through the drainage channels, reducing the pressure inside the front of the eye.