Thiazide and Thiazide-Like Diuretics Indian Medical PG Practice Questions and MCQs
Practice Indian Medical PG questions for Thiazide and Thiazide-Like Diuretics. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Thiazide and Thiazide-Like Diuretics Indian Medical PG Question 1: All of the following adverse effects can be caused by loop diuretics except :
- A. Hypomagnesemia
- B. Hyperglycemia
- C. Hypercalcemia (Correct Answer)
- D. Hyperuricemia
Thiazide and Thiazide-Like Diuretics Explanation: ***Hypercalcemia***
- Loop diuretics inhibit the reabsorption of calcium in the thick ascending limb of the loop of Henle, leading to **increased calcium excretion** and thus **hypocalcemia**, not hypercalcemia [2].
- This property makes them useful in treating conditions like hypercalcemia, but it means they do not cause hypercalcemia themselves.
*Hypomagnesemia*
- Loop diuretics inhibit magnesium reabsorption in the thick ascending limb, leading to **increased urinary magnesium excretion** and potential **hypomagnesemia** [1], [2].
- This electrolyte imbalance can contribute to cardiac arrhythmias and muscle weakness [2].
*Hyperglycemia*
- Loop diuretics, particularly in high doses, can decrease **insulin secretion** and increase **insulin resistance**, leading to **hyperglycemia**.
- This effect is generally mild but can be significant in patients with **diabetes mellitus**.
*Hyperuricemia*
- Loop diuretics compete with uric acid for secretion into the renal tubules, leading to **reduced uric acid excretion** and elevated serum uric acid levels, also known as **hyperuricemia** [1].
- This can precipitate or exacerbate **gout attacks** in susceptible individuals [1].
Thiazide and Thiazide-Like Diuretics Indian Medical PG Question 2: Mechanism of action of thiazides is by -
- A. Inhibiting Na+K+2Cl- in ascending limb of loop of henle
- B. Inhibiting Na+/Cl- symporter in DCT (Correct Answer)
- C. Inhibiting Na+/Cl- symporter in PCT
- D. Inhibiting Na+K+2Cl- in descending limb of loop of henle
Thiazide and Thiazide-Like Diuretics Explanation: **Inhibiting Na+/Cl- symporter in DCT**
- Thiazide diuretics primarily act on the **distal convoluted tubule (DCT)** of the nephron [2].
- They inhibit the **Na+/Cl- symporter** (NCC channel) on the apical membrane, preventing reabsorption of sodium and chloride ions [1], [2].
*Inhibiting Na+K+2CI- in descending limb of loop of henle*
- The descending limb of the loop of Henle is permeable to water but largely impermeable to solutes; there is no significant Na+K+2Cl- symporter activity here.
- This mechanism describes the action of loop diuretics, but they act on the **ascending** limb, not the descending limb.
*Inhibiting Na+K+2Cl- in ascending limb of loop of henle*
- This mechanism describes the action of **loop diuretics** (e.g., furosemide, bumetanide) [3].
- Loop diuretics inhibit the **Na+K+2Cl- cotransporter (NKCC2)** in the thick ascending limb of the loop of Henle, leading to significant diuresis [3].
*Inhibiting Na+/Cl- symporter in PCT*
- The **proximal convoluted tubule (PCT)** is primarily responsible for reabsorbing most of the filtered sodium, chloride, bicarbonate, and other solutes.
- While sodium is reabsorbed in the PCT, it's mainly through Na+/H+ exchangers and other mechanisms, not a specific Na+/Cl- symporter that is targeted by thiazides [2].
Thiazide and Thiazide-Like Diuretics Indian Medical PG Question 3: How do thiazides cause hypercalcemia?
- A. Decreased calcium excretion (Correct Answer)
- B. Increased parathyroid hormone secretion
- C. Decreased calcitonin secretion
- D. Increased calcium absorption
Thiazide and Thiazide-Like Diuretics Explanation: ***Decreased calcium excretion***
- Thiazides inhibit the **Na-Cl co-transporter** in the **distal convoluted tubule**, leading to increased reabsorption of calcium [1], [2].
- This increased reabsorption of calcium is mediated by a low intracellular sodium concentration, which enhances the activity of the **Na+/Ca2+ exchanger** on the basolateral membrane [1].
*Increased parathyroid hormone secretion*
- Thiazides **do not directly stimulate** parathyroid hormone (PTH) secretion; instead, they *decrease* calcium excretion, which would typically *lower* PTH levels through negative feedback.
- Elevated PTH would lead to increased bone resorption and kidney calcium reabsorption, but this is not the **primary mechanism** for thiazide-induced hypercalcemia [2].
*Decreased calcitonin secretion*
- **Calcitonin** is a hormone that *lowers* blood calcium levels, and its decrease would theoretically contribute to hypercalcemia.
- However, thiazides have **no direct effect** on calcitonin secretion, making this an unlikely primary mechanism.
*Increased calcium absorption*
- While increased calcium absorption from the gut can contribute to hypercalcemia, thiazides do **not directly increase intestinal calcium absorption**.
- Their primary action for influencing calcium levels is within the **kidney**, specifically on reabsorption, not absorption from the GI tract [1], [2].
Thiazide and Thiazide-Like Diuretics Indian Medical PG Question 4: Thiazides and loop diuretics both have opposite action on which of the following ions ?
- A. Potassium
- B. Sodium
- C. Chloride
- D. Calcium (Correct Answer)
Thiazide and Thiazide-Like Diuretics Explanation: ***Calcium***
- Thiazide diuretics **increase calcium reabsorption** in the distal convoluted tubule, leading to decreased urinary calcium excretion.
- Loop diuretics **decrease calcium reabsorption** in the thick ascending limb of the loop of Henle, resulting in increased urinary calcium excretion.
*Potassium*
- Both thiazide and loop diuretics can cause **hypokalemia** by increasing potassium excretion in the urine.
- This is due to increased sodium delivery to the collecting duct, which stimulates potassium secretion.
*Sodium*
- Both thiazide and loop diuretics inhibit sodium reabsorption at different sites in the nephron, leading to **increased urinary sodium excretion** (natriuresis).
- This is their primary mechanism of action for diuresis.
*Chloride*
- Both thiazide and loop diuretics inhibit **chloride reabsorption** as they block specific sodium-chloride cotransporters.
- Thiazides inhibit the Na-Cl cotransporter in the DCT, while loop diuretics inhibit the Na-K-2Cl cotransporter in the thick ascending limb.
Thiazide and Thiazide-Like Diuretics Indian Medical PG Question 5: Which electrolyte shows the most significant increase in urinary excretion within 24 hours of initiating thiazide diuretic therapy for hypertension?
- A. Sodium (Correct Answer)
- B. Potassium
- C. Magnesium
- D. Calcium
Thiazide and Thiazide-Like Diuretics Explanation: ***Sodium***
- Thiazide diuretics primarily act on the **distal convoluted tubule** by inhibiting the **Na+/Cl- cotransporter**, leading to increased excretion of **sodium** and water [1].
- The initial and most significant pharmacological effect of thiazides is to promote **natriuresis**, removing excess sodium from the body [2].
- Within **24 hours**, sodium excretion shows the most pronounced increase, which is the primary mechanism for blood pressure reduction [2].
*Potassium*
- While thiazides do cause **potassium excretion**, this effect is less significant than sodium excretion initially and is partly due to increased flow to the collecting duct and elevated aldosterone levels [2].
- Hypokalemia is a known side effect of long-term thiazide use, but the **immediate increase in urinary sodium** is more pronounced.
*Magnesium*
- Thiazide diuretics are known to cause **increased urinary excretion of magnesium**, which can lead to hypomagnesemia with chronic use [3].
- However, the initial increase in magnesium excretion is generally **less pronounced** compared to sodium excretion within the first 24 hours of therapy.
*Calcium*
- Uniquely among diuretics, thiazides **decrease** urinary calcium excretion, promoting calcium retention and reabsorption in the distal tubule [1], [3].
- This is why thiazides are sometimes used therapeutically in **hypercalciuric nephrolithiasis** and can cause hypercalcemia as a side effect.
- Calcium excretion is **reduced**, not increased, making this the opposite of the correct answer.
Thiazide and Thiazide-Like Diuretics Indian Medical PG Question 6: Which diuretic is known to cause the maximum potassium loss?
- A. Spironolactone
- B. Furosemide (Correct Answer)
- C. Thiazide diuretics
- D. Acetazolamide
Thiazide and Thiazide-Like Diuretics Explanation: ***Furosemide***
- Furosemide is a **loop diuretic** that inhibits the Na-K-2Cl cotransporter in the **thick ascending limb of the loop of Henle**, leading to significant excretion of sodium, chloride, potassium, and water.
- Its potent diuresis and impact on potassium reabsorption result in a **high risk of hypokalemia**.
*Thiazide*
- Thiazide diuretics inhibit the **Na-Cl cotransporter** in the **distal convoluted tubule**, causing moderate sodium and water excretion, and some potassium loss.
- While they can cause hypokalemia, their effect on potassium excretion is generally **less pronounced than loop diuretics**.
*Acetazolamide*
- Acetazolamide is a **carbonic anhydrase inhibitor** that acts primarily in the **proximal tubule**, inhibiting bicarbonate reabsorption and leading to increased excretion of bicarbonate, sodium, potassium, and water.
- The potassium loss is due to increased delivery of sodium to the collecting duct, leading to enhanced potassium secretion, but it is typically **less severe than with loop diuretics**.
*Spironolactone*
- Spironolactone is a **potassium-sparing diuretic** that acts as an **aldosterone antagonist** in the collecting duct, inhibiting sodium reabsorption and potassium secretion.
- Instead of causing potassium loss, spironolactone actually **conserves potassium** and can lead to hyperkalemia.
Thiazide and Thiazide-Like Diuretics Indian Medical PG Question 7: All of the following diuretics increase K+ excretion EXCEPT:
- A. Acetazolamide
- B. Triamterene (Correct Answer)
- C. Thiazide
- D. Furosemide
Thiazide and Thiazide-Like Diuretics Explanation: ***Triamterene***
- **Triamterene** is a **potassium-sparing diuretic** that blocks epithelial sodium channels (ENaC) in the collecting duct, thereby reducing sodium reabsorption and potassium secretion.
- Unlike most other diuretics, it causes **decreased K+ excretion** and can lead to hyperkalemia.
*Acetazolamide*
- **Acetazolamide** is a **carbonic anhydrase inhibitor** that acts in the proximal tubule, inhibiting bicarbonate reabsorption.
- This leads to increased delivery of sodium and bicarbonate to the collecting duct, which enhances **potassium secretion** and increases K+ excretion.
*Thiazide*
- **Thiazide diuretics** (e.g., hydrochlorothiazide) act by inhibiting the Na+/Cl- cotransporter in the **distal convoluted tubule**.
- This increases the delivery of sodium to the collecting duct, which stimulates the exchange of sodium for **potassium**, leading to increased K+ excretion and hypokalemia.
*Furosemide*
- **Furosemide** is a **loop diuretic** that inhibits the Na+/K+/2Cl- cotransporter in the **thick ascending limb of the loop of Henle**.
- This prevents the reabsorption of these ions, leading to increased delivery of sodium to the collecting duct, which promotes **potassium secretion** and increased K+ excretion.
Thiazide and Thiazide-Like Diuretics Indian Medical PG Question 8: Which diuretic is most likely to cause hyponatremia by impairing free water excretion?
- A. Loop diuretics
- B. Acetazolamide
- C. Amiloride
- D. Thiazide diuretics (Correct Answer)
Thiazide and Thiazide-Like Diuretics Explanation: ***Thiazide diuretics***
- **Thiazide diuretics** inhibit the **Na-Cl cotransporter in the distal convoluted tubule (DCT)**, impairing the kidney's ability to dilute urine and excrete free water
- This impaired urinary dilution leads to **water retention relative to sodium**, resulting in **dilutional hyponatremia**
- **Most common in elderly patients**, those on low-salt diets, or with pre-existing volume depletion
- **Mechanism**: By blocking sodium reabsorption in the DCT (a key site for urinary dilution), thiazides prevent the generation of free water, leading to hyponatremia when water intake continues
*Loop diuretics*
- **Loop diuretics** inhibit the **Na-K-2Cl cotransporter in the thick ascending limb of Henle**, causing significant diuresis
- They impair the medullary concentration gradient, **enhancing free water excretion**
- **Less likely to cause hyponatremia** compared to thiazides because they promote rather than impair free water clearance
- When hyponatremia occurs with loop diuretics, it's usually due to concurrent SIADH or excessive free water intake
*Acetazolamide*
- **Acetazolamide** is a **carbonic anhydrase inhibitor** acting primarily on the **proximal tubule**
- Causes **bicarbonate and sodium excretion**, leading to mild diuresis
- Main side effect is **metabolic acidosis** (type 2 RTA)
- **Does not significantly impair free water excretion**, making hyponatremia uncommon
*Amiloride*
- **Amiloride** is a **potassium-sparing diuretic** that blocks **epithelial sodium channels (ENaC) in the collecting duct**
- Weak diuretic effect, primarily used to prevent potassium loss
- **Does not impair urinary dilution mechanisms**, so hyponatremia is rare
- Main concern is **hyperkalemia**, especially with ACE inhibitors or in renal insufficiency
Thiazide and Thiazide-Like Diuretics Indian Medical PG Question 9: In which segment of the nephron does ethacrynic acid exert its diuretic action?
- A. Proximal convoluted tubule
- B. Collecting duct
- C. Distal convoluted tubule
- D. Thick ascending limb of loop of Henle (Correct Answer)
Thiazide and Thiazide-Like Diuretics Explanation: ***Thick ascending limb of loop of Henle***
- Ethacrynic acid is a **loop diuretic** that acts by inhibiting the **Na+-K+-2Cl- cotransporter** (NKCC2) in the luminal membrane of the thick ascending limb.
- This inhibition prevents the reabsorption of ions, leading to increased excretion of water, sodium, chloride, and potassium.
*Proximal convoluted tubule*
- The proximal convoluted tubule is the primary site of reabsorption of most filtered substances, but loop diuretics like ethacrynic acid do not primarily act here.
- Carbonic anhydrase inhibitors and SGLT2 inhibitors are examples of diuretics that exert their effects in this segment.
*Collecting duct*
- The collecting duct is the site where aldosterone antagonists (e.g., spironolactone) and epithelial sodium channel (ENaC) inhibitors (e.g., amiloride, triamterene) exert their diuretic effects.
- Its primary role involves fine-tuning water reabsorption under the influence of ADH and regulating potassium excretion.
*Distal convoluted tubule*
- Thiazide diuretics primarily act in the distal convoluted tubule by inhibiting the **Na+-Cl- cotransporter** (NCC).
- This segment is responsible for further diluting the urine and reabsorbing a small percentage of filtered sodium and chloride.
Thiazide and Thiazide-Like Diuretics Indian Medical PG Question 10: A patient on lithium therapy developed hypertension and was started on a thiazide diuretic. After a few days, he developed coarse tremors and other symptoms suggestive of lithium toxicity. What is the probable mechanism of interaction between thiazide diuretics and lithium?
- A. Thiazide increases the tubular reabsorption of lithium (Correct Answer)
- B. Thiazide inhibits the metabolism of lithium
- C. Thiazides act as an add-on drug to lithium
- D. None of the above
Thiazide and Thiazide-Like Diuretics Explanation: ***Thiazide increases the tubular reabsorption of lithium***
- Thiazide diuretics cause a decrease in sodium reabsorption in the distal convoluted tubule, leading to increased sodium excretion in urine.
- The kidneys, in an attempt to conserve sodium, increase reabsorption in the proximal tubule. Because **lithium** is reabsorbed similarly to sodium in the proximal tubule, this increased reabsorption also affects lithium, leading to a rise in its plasma concentration and toxicity.
*Thiazide inhibits the metabolism of lithium*
- Lithium is primarily excreted by the kidneys and is not significantly metabolized in the body.
- Thiazide diuretics do not affect enzyme systems responsible for drug metabolism.
*Thiazides act as an add on the drug to lithium*
- This statement is vague and does not explain a mechanism of interaction leading to toxicity.
- While both drugs might be prescribed concurrently for different conditions, "add on" does not describe a pharmacological interaction causing altered drug levels.
*None of the above*
- This option is incorrect because a clear and well-understood mechanism for the interaction between thiazide diuretics and lithium exists.
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