Available Agents and Dosing Frequency
The topical CAI agents, dorzolamide and brinzolamide, are available for long-term treatment of elevated IOP and are associated with fewer systemic adverse effects than are the systemic CAIs. In the United States, these agents are currently approved for use 3 times daily, but most clinicians prescribe them for twice-daily use in many patients. Dosing 3 times per day dosing results in slightly greater IOP reduction. For patients taking an oral CAI at a full dose and the appropriate dosing frequency, there is no advantage to adding a topical CAI.
Systemic CAIs can be given orally or intravenously and are most useful in patients who present with severely elevated IOP or as a temporizing measure until surgery can be performed. Oral CAIs begin to act within 1 hour of administration, with maximal effect within 2–4 hours, whereas intravenous CAIs begin to act within 15 minutes. Sustained-release acetazolamide can reach peak effect within 3–6 hours of administration. Because of the adverse effects of systemic CAIs, however, long-term therapy should be reserved for patients whose IOP is not controlled with topical therapy and who have refused surgery or in whom surgery would be inappropriate.
The most commonly used oral CAIs are acetazolamide and methazolamide. Methazolamide has a longer duration of action and is less bound to serum protein than is acetazolamide; however, it is also less effective than acetazolamide. Methazolamide and sustained-release acetazolamide are the best tolerated of the systemic CAIs. Methazolamide is metabolized by the liver. Acetazolamide, which is not metabolized, is excreted by the kidney; it must be used with caution and at an adjusted dose in patients with renal insufficiency.
Because oral CAIs are potent medications that are associated with significant adverse effects, the lowest dose that reduces the IOP to an acceptable range should be used. Methazolamide is often effective in doses as low as 25–50 mg, given 2 or 3 times daily. Sustained-release formulations of acetazolamide may have fewer adverse effects than its standard formulation. The typical adult dosage of acetazolamide is 250 mg 4 times daily for the standard formulations or 500 mg twice daily for the sustained-release formulation.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.