Anesthesia: Carbonic Anhydrase Inhibitors

CARBONIC ANHYDRASE INHIBITORS

Carbonic anhydrase inhibitors such as acetazol-amide (Diamox) interfere with Na⁺ reabsorption and H⁺ secretion in proximal tubules. They are weak diuretics because the former effect is limited by the reabsorptive capacities of more distal segments of nephrons. Nonetheless, these agents significantly interfere with H⁺ secretion in the proximal tubule and impair HCO₃⁻ reabsorption.

Uses

A. Correction of Metabolic Alkalosis in Edematous Patients

Carbonic anhydrase inhibitors often potentiate the effects of other diuretics.

B. Alkalinization of Urine

Alkalinization enhances urinary excretion of weakly acidic compounds such as uric acid.

C. Reduction of Intraocular Pressure

Inhibition of carbonic anhydrase in the ciliary pro-cesses reduces the formation of aqueous humor and, secondarily, intraocular pressure. Carbonic anhy-drase inhibitors, including oral or intravenous acet-azolamide, oral methazolamide (Neptazane), and ophthalmic topical brinzolamide (Azopt) and dorzol-amide (Trusopt) are often used to treat glaucoma.

Intravenous Dosage

For acetazolamide, the intravenous dose is 250– 500 mg.

Side Effects

Carbonic anhydrase inhibitors generally produce only a mild hyperchloremic metabolic acidosis because of an apparently limited effect on the distal nephron. Large doses of acetazolamide have been reported to cause drowsiness, paresthesias, and con-fusion. Alkalinization of the urine can interfere with the excretion of amine drugs, such as quinidine. Acetazolamide is frequently used for prophylaxis against mountain sickness.