Diuretics Practice Questions

Q: Potassium secretion is decreased by action on the late distal tubule by which agent?

Spironolactone. ***Spironolactone*** - Spironolactone is a **potassium-sparing diuretic** that acts as an **aldosterone antagonist** in the **late distal tubule and collecting ducts**. - By blocking aldosterone receptors, it **decreases sodium reabsorption** and **inhibits potassium secretion**. - This is the only option that specifically acts on the late distal tubule to decrease potassium secretion. *Thiazide* - Thiazide diuretics act on the **early distal convoluted tubule (DCT)**, not the late distal tubule, to inhibit the Na+/Cl− cotransporter. - This typically leads to **increased potassium secretion** indirectly, as increased sodium delivery to the collecting duct drives potassium excretion. *Furosemide* - Furosemide is a **loop diuretic** that acts on the **thick ascending limb of the loop of Henle**, inhibiting the Na+/K+/2Cl− cotransporter. - Its action results in a significant increase in **potassium excretion** due to increased sodium delivery to the collecting duct. *Acetazolamide* - Acetazolamide is a **carbonic anhydrase inhibitor** that primarily acts on the **proximal convoluted tubule**. - It causes increased excretion of bicarbonate, sodium, and potassium, thus **increasing potassium secretion**, not decreasing it.

Q: A 50-year-old man has a history of frequent episodes of renal colic with high calcium renal stones. The most useful diuretic in the treatment of recurrent calcium stones is:

Hydrochlorothiazide. ***Hydrochlorothiazide*** - **Thiazide diuretics** reduce urinary calcium excretion by increasing calcium reabsorption in the distal convoluted tubule. - This mechanism makes them effective in preventing the recurrence of **calcium oxalate** and **calcium phosphate kidney stones**. *Furosemide* - **Loop diuretics** like furosemide increase urinary calcium excretion, which would *aggravate* rather than prevent calcium stone formation. - This effect is due to inhibiting sodium-potassium-chloride reabsorption in the **loop of Henle**, thereby reducing calcium reabsorption. *Spironolactone* - **Spironolactone** is a potassium-sparing diuretic that acts as an aldosterone antagonist, primarily affecting sodium and potassium balance. - It does not significantly impact urinary calcium excretion, and therefore, it is **not indicated** for the prevention of calcium renal stones. *Acetazolamide* - **Acetazolamide** is a carbonic anhydrase inhibitor that increases bicarbonate excretion and causes a metabolic acidosis. - It increases urinary pH and can potentially *promote* the formation of calcium phosphate stones in susceptible individuals.

Q: Hypercalcemia is caused by all except:

Loop diuretics. Hypercalcemia is caused by all except: ***Loop diuretics*** - **Loop diuretics** promote the urinary excretion of calcium by inhibiting the reabsorption of calcium in the thick ascending limb of the loop of Henle [3]. - This effect leads to a **decrease** in serum calcium levels and thus do not cause hypercalcemia. [3] *Lithium* - **Lithium** can cause hypercalcemia by increasing the set point for calcium sensing in the parathyroid glands, leading to increased parathyroid hormone (PTH) secretion. - This results in a mild, chronic hypercalcemia, often in the context of **secondary hyperparathyroidism**. *Vitamin D intoxication* - **Vitamin D intoxication** leads to excessive absorption of calcium from the gut and increased bone resorption, both contributing to hypercalcemia [1]. - High levels of vitamin D cause hypercalcemia that **suppresses PTH secretion** through negative feedback, resulting in hypercalcemia with inappropriately low PTH levels. *Thiazides* - **Thiazide diuretics** can cause mild hypercalcemia by increasing renal tubular reabsorption of calcium [2]. - They enhance calcium reabsorption in the **distal convoluted tubule**, leading to a slight elevation in serum calcium [2], [3].

Q: Which of the following statements about the PRIMARY mechanism of action of acetazolamide is correct?

Reversible inhibitor of carbonic anhydrase. ***Reversible inhibitor of carbonic anhydrase*** - Acetazolamide is a **carbonic anhydrase inhibitor** that primarily acts by reducing the reabsorption of bicarbonate in the proximal tubule of the kidney. - This inhibition leads to increased urinary excretion of **bicarbonate, sodium, and water**, ultimately reducing intraocular pressure, intracranial pressure, and systemic fluid retention. *It decreases potassium excretion* - Acetazolamide actually **increases potassium excretion** indirectly by increasing the delivery of sodium and bicarbonate to the collecting duct, which enhances potassium secretion. - This can lead to **hypokalemia** with prolonged use. *It causes metabolic alkalosis* - Acetazolamide causes **metabolic acidosis**, not alkalosis, because it inhibits the reabsorption of bicarbonate in the renal tubules, leading to increased bicarbonate excretion and a decrease in serum bicarbonate levels. - This effect makes it useful in treating metabolic alkalosis, but it does not cause it. *Has structural resemblance to penicillins* - Acetazolamide is a **sulfonamide derivative** and does not have a structural resemblance to penicillins. - Its mechanism of action is completely distinct from that of antibiotics in the penicillin class.

Q: Select the diuretic that is most effective in acute angle-closure glaucoma.

Mannitol. ***Mannitol*** - **Mannitol** is an osmotic diuretic that creates an osmotic gradient, drawing fluid from the eye into the bloodstream, thereby **rapidly reducing intraocular pressure (IOP)**. - Its quick onset of action and potent IOP-lowering effect make it the **drug of choice for acute angle-closure glaucoma** when rapid pressure reduction is critical. *Furosemide* - **Furosemide** is a loop diuretic that primarily acts on the renal tubules to increase urine output, with **minimal direct effect on intraocular pressure**. - While it can lower systemic blood pressure, its efficacy in **rapidly reducing elevated IOP in acute glaucoma is limited** compared to osmotic agents. *Amiloride* - **Amiloride** is a potassium-sparing diuretic that works in the collecting ducts of the kidneys and is primarily used for **hypertension and heart failure**, often in combination with other diuretics. - It does not have a significant or rapid effect on **intraocular pressure**, making it ineffective for acute angle-closure glaucoma. *Indapamide* - **Indapamide** is a thiazide-like diuretic that acts on the distal convoluted tubule and is primarily used for the treatment of **hypertension and edema**. - It has a slower onset of action and **does not effectively reduce intraocular pressure** in acute settings, making it unsuitable for acute angle-closure glaucoma.

Question 1

Potassium secretion is decreased by action on the late distal tubule by which agent?

Accepted Answer

Spironolactone

Answer

Thiazide

Answer

Furosemide

Answer

Acetazolamide

Question 2

A 50-year-old man has a history of frequent episodes of renal colic with high calcium renal stones. The most useful diuretic in the treatment of recurrent calcium stones is:

Accepted Answer

Hydrochlorothiazide

Answer

Furosemide

Answer

Acetazolamide

Answer

Spironolactone

Question 3

Hypercalcemia is caused by all except:

Accepted Answer

Loop diuretics

Answer

Lithium

Answer

Thiazides

Answer

Vitamin D intoxication

Question 4

Which of the following statements about the PRIMARY mechanism of action of acetazolamide is correct?

Accepted Answer

Reversible inhibitor of carbonic anhydrase

Answer

It causes metabolic alkalosis

Answer

It decreases potassium excretion

Answer

Has structural resemblance to penicillins

Question 5

Select the diuretic that is most effective in acute angle-closure glaucoma.

Accepted Answer

Mannitol

Answer

Furosemide

Answer

Amiloride

Answer

Indapamide

Diuretics — MCQs

Diuretics — MCQs

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