How acetazolamide works
Acetazolamide is a carbonic anhydrase inhibitor. In the eye it reduces the production of aqueous humor and lowers intraocular pressure, which is why it is given intravenously in acute angle-closure glaucoma. The same enzyme is active in the proximal tubule of the kidney, where it helps reabsorb bicarbonate. Blocking renal carbonic anhydrase increases urinary loss of bicarbonate and potassium, producing hypokalemia and metabolic acidosis, so serum potassium is the value to monitor most closely.
Why potassium is lost
When bicarbonate reabsorption is blocked in the proximal tubule, more sodium bicarbonate reaches the distal nephron. There, sodium is exchanged for potassium, so potassium is excreted in the urine. The result is hypokalemia together with a hyperchloremic metabolic acidosis. The normal serum potassium range is 3.5–5.0 mEq/L. Low potassium can cause muscle weakness, cramps, and dangerous dysrhythmias, especially in older clients or those taking other potassium-wasting drugs.
| Lab value | Effect of acetazolamide | Priority? |
|---|
| Serum potassium | Falls (hypokalemia) | Highest |
| Serum calcium | Not a main disturbance | No |
| Serum amylase | Not typically affected | No |
| Platelet count | Blood dyscrasias are rare | No |
Other adverse effects to watch
Besides electrolyte and acid-base changes, acetazolamide commonly causes paresthesia (tingling of fingers, toes, and around the mouth), fatigue, altered taste, and increased urination. It can promote kidney stones, and because it is a sulfonamide derivative, the nurse checks for a sulfa allergy. Rare blood dyscrasias have been reported, which is why platelets are not the priority but may be checked during prolonged use.
Watch out! Diuretics that act on different parts of the nephron can share the same electrolyte problem. Carbonic anhydrase inhibitors, like loop and thiazide diuretics, waste potassium.
Exam takeaway
Key point! Acetazolamide causes hypokalemia and metabolic acidosis; monitor serum potassium during therapy. Teach the client to report tingling, weakness, flank pain, or palpitations.