A 30-year-old woman is evaluated for almost daily headaches and intermittent blurry vision. Medical history includes obesity but no other chronic conditions. Physical examination shows bilateral symmetric papilledema. There are no other focal neurological deficits. Brain imaging is normal, and blood cell counts and serum chemistry studies are within normal limits. Lumbar puncture reveals elevated opening pressure, and idiopathic intracranial hypertension is diagnosed. Weight loss is advised, and the patient is prescribed acetazolamide therapy. Which of the following changes are most likely to occur in this patient over the next several days due to the medication?

Question

Quizplus · Accepted Answer

11ec160b_3c71_1cee_9249_ff26214257c0_MD0001_00 Acetazolamide is a carbonic anhydrase inhibitor that acts as a weak diuretic. The drug also reduces intracranial pressure and improves symptoms in patients with idiopathic intracranial hypertension. This effect occurs independent of the kidneys and likely results from a decreased rate of cerebrospinal fluid production by the choroid plexus. Carbonic anhydrase inhibitors block reabsorption of sodium bicarbonate (NaHCO₃) in the proximal tubule, leading to increased excretion of HCO₃^-. This alkalinizes the urine (increased pH) while reducing blood pH to create mild metabolic acidosis. The overall diuretic effect is weak because most of the Na⁺ blocked from reabsorption in the proximal tubule is reabsorbed more distally. The distal reabsorption of Na⁺ stimulates increased K⁺ excretion (and relatively insignificant increased H⁺ excretion), leading to increased urine potassium and mild hypokalemia. There is no significant effect on Ca²⁺ or other electrolytes (Choice A). In response to the mild metabolic acidosis, ventilation is increased to facilitate CO₂ removal and decrease blood PaCO₂ (compensatory respiratory alkalosis). (Choice C) Potassium-sparing diuretics (eg, spironolactone) block Na⁺ reabsorption in the collecting duct while increasing the reabsorption of K⁺ and H⁺. This decreases urine potassium and increases urine pH. Mild metabolic acidosis is generated with compensatory respiratory alkalosis. Ca²⁺ and other electrolytes are not significantly affected. (Choice D) Loop diuretics (eg, furosemide) block the Na⁺K⁺2Cl^- transporter in the ascending loop of Henle. This causes potent excretion of Na⁺, K⁺, and Cl^- (increased urine potassium) and impairs passive Ca²⁺ reabsorption, decreasing serum calcium. There is also aldosterone-mediated H⁺ loss, and the Cl^- depletion impairs HCO₃^-excretion, leading to decreased urine pH and metabolic alkalosis with compensatory respiratory acidosis (increased PaCO₂). (Choice E) Thiazide diuretics (eg, hydrochlorothiazide) block the Na⁺Cl^- transporter in the distal convoluted tubule. Ca²⁺ reabsorption is increased, leading to increased serum calcium. Otherwise, the effects are the same as those with loop diuretics but with less potency. Educational objective: Carbonic anhydrase inhibitors (eg, acetazolamide) are weak diuretics that block reabsorption of sodium bicarbonate (NaHCO₃) in the proximal tubule. The main effect is increased HCO₃^- excretion, leading to increased urine pH, mild metabolic acidosis (with compensatory respiratory alkalosis), and mild hypokalemia.

A 30-Year-Old Woman Is Evaluated for Almost Daily Headaches and Intermittent