Why would we dose acetazolamide (Diamox) 500 mg ER?

• A. For longer-term therapy
• B. For acute IOP lowering
• C. To prevent kidney stones
• D. To treat metabolic acidosis

Answer: (C)

Acetazolamide lowers aqueous production by inhibiting carbonic anhydrase in the eye, but the extended-release 500 mg dose is chosen here for a different reason: it alkalinizes urine over a longer period. Blocking proximal tubule bicarbonate reabsorption causes bicarbonate to be wasted in the urine, making the urine more alkaline. Alkaline urine helps prevent uric acid stones, which form in acidic urine, by keeping uric acid dissolved. The extended-release formulation provides a steady, once-daily dosing approach for chronic stone prevention. This is not the best choice for acutely lowering intraocular pressure, and it typically does not “treat” metabolic acidosis—it can actually contribute to a metabolic acidosis as a side effect.