Carboanhydrase inhibitors

Carbonic anhydrase, present mainly in cells of the proximal tubule epithelium, is responsible for the excretion of hydrogen ions (H+). Inhibition of this excretion leads to decreased reabsorption of bicarbonate (HCO3) and sodium ions (Na+) and thus decreased reabsorption of water; increased water is excreted. However, because this mechanism occurs primarily in the proximal tubule, increased water is reabsorbed in the distal tubule in a compensatory manner, which reduces the effect of carbonic anhydrase inhibitors.

In addition, the increased loss of Na+ leads to increased retention of Cl- and increased excretion of K+. This results in hypokalemia and hyperchloremic metabolic acidosis, which leads to increased availability of H+ in the kidney and thus drastically reduces the effect of carbonic anhydrase.

Individual substances

• Acetazolamide
• Dorzolamide
• Other carbonic anhydrase inhibitors

Carboanhydrase inhibitors are only weakly effective diuretics and are no longer used as such. Carboanhydrase inhibitors reduce the ciliary production of aqueous humor. This is the reason for the current indication: therapy of glaucoma.

In case of impaired renal or hepatic function, carbonic anhydrase inhibitors must not be used. In the presence of hepatic insufficiency, carbonic anhydrase inhibitors increase the risk of hepatic coma due to ammonia accumulation.

In case of allergy to sulfonamides, carbonic anhydrase inhibitors should not be used. In lactating patients, treatment with carbonic anhydrase inhibitors should be considered only after weaning.