Diuretics — MCQs

Diuretics Indian Medical PG Practice Questions and MCQs

Question 101: Thiazide diuretics do not produce which of the following adverse effects?

A. Hypoglycemia (Correct Answer)
B. Hyponatremia
C. Hypokalemia
D. Hyperuricemia

Explanation: **Explanation:** Thiazide diuretics are known for causing a variety of metabolic disturbances, but **Hypoglycemia** is not one of them. In fact, Thiazides are notorious for causing **Hyperglycemia**. **1. Why Hypoglycemia is the correct answer:** Thiazides impair glucose tolerance by inhibiting insulin release from the pancreas (partially due to hypokalemia, which hyperpolarizes beta cells) and decreasing peripheral glucose utilization. Therefore, they cause an *increase* in blood sugar levels, making "hypoglycemia" the incorrect clinical effect. **2. Analysis of Incorrect Options:** * **Hyponatremia (B):** Thiazides inhibit the $Na^+/Cl^-$ symporter in the distal convoluted tubule. They increase sodium excretion while the body’s ability to dilute urine is impaired, frequently leading to low serum sodium. * **Hypokalemia (C):** Increased sodium delivery to the collecting ducts stimulates the exchange of $Na^+$ for $K^+$, leading to significant potassium loss in the urine. * **Hyperuricemia (D):** Thiazides compete with uric acid for the organic acid secretory secretory pathway in the proximal tubule. This leads to uric acid retention, which can precipitate acute gouty arthritis. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Thiazide side effects:** **"Hyper GLUC"** – **G**lycemia, **L**ipidemia (Hyperlipidemia), **U**ricemia, and **C**alcemia (Hypercalcemia). * **Calcium Sparing:** Unlike Loop diuretics ("Loops Lose Calcium"), Thiazides *increase* calcium reabsorption and are used clinically to prevent calcium-containing renal stones. * **Drug of Choice:** Thiazides are often the first-line treatment for essential hypertension in patients without co-morbidities.

Question 102: A 68-year-old woman presents with symptoms and signs of congestive heart failure. Which of the following is a contraindication to the use of furosemide?

A. Hypoalbuminemia
B. Oliguria
C. Acidosis
D. A history of rash with trimethoprim-sulfamethoxazole (Correct Answer)

Explanation: ### Explanation **Correct Option: D. A history of rash with trimethoprim-sulfamethoxazole** The correct answer is based on the concept of **cross-reactivity among sulfonamide-derived drugs**. Furosemide is a sulfonamide derivative. Trimethoprim-sulfamethoxazole (Bactrim/Septra) contains sulfamethoxazole, a sulfonamide antibiotic. Patients who have experienced an allergic reaction (like a rash, urticaria, or Stevens-Johnson Syndrome) to sulfonamide antibiotics may exhibit cross-reactivity with non-antibiotic sulfonamides, including loop diuretics (furosemide, bumetanide), thiazides, and sulfonylureas. While the clinical risk of cross-reactivity is sometimes debated, for the purpose of exams like NEET-PG, a known sulfonamide allergy is a classic contraindication for furosemide. **Why other options are incorrect:** * **A. Hypoalbuminemia:** Furosemide is highly protein-bound (to albumin). In hypoalbuminemia, the delivery of furosemide to the proximal tubule is reduced, leading to "diuretic resistance." It is not a contraindication; rather, it may necessitate higher doses or co-administration with albumin. * **B. Oliguria:** Furosemide is frequently used to treat oliguria in the setting of acute kidney injury or fluid overload to "convert" oliguric renal failure to non-oliguric failure. It is only contraindicated in **anuria** (complete absence of urine production). * **C. Acidosis:** Furosemide actually tends to cause **contraction alkalosis** (hypokalemic metabolic alkalosis). It is not contraindicated in acidosis; in fact, it does not worsen the acidotic state directly. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Inhibits the **Na+/K+/2Cl- symporter** in the Thick Ascending Limb (TAL) of the Loop of Henle. * **Drug of Choice:** Furosemide is the DOC for **acute pulmonary edema** due to its rapid action and venodilatory properties. * **Side Effects Mnemonic (OH DANG!):** **O**totoxicity, **H**ypokalemia, **D**ehydration, **A**llergy (Sulfa), **N**ephritis (Interstitial), **G**out (Hyperuricemia). * **Ethacrynic Acid:** The only loop diuretic that is **not** a sulfonamide; it is the alternative for patients with sulfa allergies but carries a higher risk of ototoxicity.

Question 103: Hypokalemia is seen with which of the following?

A. Frusemide
B. Cortisol
C. Amiloride
D. Addison's disease (Correct Answer)

Explanation: ### Explanation The question asks to identify the condition or drug associated with **Hypokalemia** (low serum potassium). #### **1. Why the Correct Answer is Right (Addison’s Disease)** Wait, there appears to be a **discrepancy in the provided key**. In clinical medicine, **Addison’s disease** (Primary Adrenocortical Insufficiency) is characterized by a deficiency of aldosterone. Since aldosterone normally promotes $K^+$ excretion, its absence leads to **Hyperkalemia**, not hypokalemia. However, if we analyze the options based on standard pharmacological principles: * **Frusemide (Option A)** and **Cortisol (Option B)** both cause **Hypokalemia**. * **Amiloride (Option C)** and **Addison’s disease (Option D)** cause **Hyperkalemia**. *Note: If the question intended to ask for "Hyperkalemia," then Addison's Disease and Amiloride would be correct. If the question asks for "Hypokalemia," then Frusemide and Cortisol are the correct answers.* #### **2. Analysis of Options** * **A. Frusemide:** A loop diuretic that inhibits the $Na^+-K^+-2Cl^-$ symporter. It increases distal sodium delivery, leading to increased $K^+$ secretion and **Hypokalemia**. * **B. Cortisol:** Has mineralocorticoid activity. It acts on the distal tubule to reabsorb $Na^+$ and excrete $K^+$, leading to **Hypokalemia** (as seen in Cushing’s syndrome). * **C. Amiloride:** A potassium-sparing diuretic that blocks epithelial sodium channels (ENaC) in the collecting duct. It prevents $K^+$ secretion, leading to **Hyperkalemia**. * **D. Addison’s Disease:** Results in hypoaldosteronism. Lack of aldosterone prevents $K^+$ excretion, classically causing **Hyperkalemia**, hyponatremia, and metabolic acidosis. #### **3. High-Yield Clinical Pearls for NEET-PG** * **Diuretics causing Hypokalemia:** Loop diuretics (Frusemide) and Thiazides. * **Diuretics causing Hyperkalemia:** Spironolactone, Eplerenone, Amiloride, and Triamterene. * **Endocrine causes of Hypokalemia:** Conn’s Syndrome (Primary Hyperaldosteronism), Cushing’s Syndrome. * **Endocrine causes of Hyperkalemia:** Addison’s Disease, Type IV Renal Tubular Acidosis.

Question 104: Vasopressin antagonists act on which part of the nephron?

A. Proximal convoluted tubule
B. Distal convoluted tubule
C. Cortical collecting tubule
D. Medullary collecting duct (Correct Answer)

Explanation: **Explanation:** Vasopressin (Antidiuretic Hormone/ADH) antagonists, also known as **Vaptans** (e.g., Tolvaptan, Conivaptan), exert their primary diuretic effect by blocking **V2 receptors**. These receptors are located on the basolateral membrane of the principal cells in the **medullary collecting duct**. **Mechanism of Action:** Under normal physiological conditions, ADH binds to V2 receptors, triggering the insertion of **Aquaporin-2 (AQP2)** water channels into the apical membrane. This allows for free water reabsorption. By antagonizing these receptors, Vaptans prevent water reabsorption, leading to **aquaresis** (excretion of solute-free water) without significant loss of electrolytes like sodium or potassium. **Analysis of Options:** * **A. Proximal Convoluted Tubule:** This is the site of action for Carbonic Anhydrase inhibitors (Acetazolamide) and SGLT2 inhibitors. * **B. Distal Convoluted Tubule:** This is the site of action for Thiazide diuretics, which inhibit the Na+-Cl- symporter. * **C. Cortical Collecting Tubule:** While some V2 receptors exist here, the **medullary** portion of the collecting duct has the highest density of these receptors and is the critical site for establishing the final urine concentration. Potassium-sparing diuretics (Amiloride, Spironolactone) act primarily in the cortical segment. **NEET-PG High-Yield Pearls:** * **Indications:** Vaptans are the treatment of choice for **SIADH** and are used in hypervolemic hyponatremia (e.g., CHF, Cirrhosis). * **Tolvaptan:** Oral, selective V2 antagonist. * **Conivaptan:** IV, non-selective (blocks both V1a and V2 receptors). * **Side Effect:** Rapid correction of hyponatremia with Vaptans carries a risk of **Osmotic Demyelination Syndrome (Central Pontine Myelinolysis).**

Question 105: Which diuretic agent is most useful in the treatment of recurrent calcium stones?

A. Mannitol
B. Furosemide
C. Spironolactone
D. Hydrochlorothiazide (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Hydrochlorothiazide** **Mechanism and Rationale:** Thiazide diuretics (like Hydrochlorothiazide) are the drugs of choice for preventing recurrent calcium oxalate stones. Their effectiveness lies in their ability to **decrease urinary calcium excretion (hypocalciuria)**. Thiazides inhibit the $Na^+/Cl^-$ symporter in the Distal Convoluted Tubule (DCT). This reduction in intracellular sodium enhances the activity of the $Na^+/Ca^{2+}$ exchanger on the basolateral membrane, which in turn creates a gradient that promotes **increased reabsorption of calcium** from the tubular lumen into the blood. By lowering the concentration of calcium in the urine, the likelihood of stone precipitation is significantly reduced. **Why the other options are incorrect:** * **A. Mannitol:** An osmotic diuretic used primarily to reduce intracranial or intraocular pressure. It does not specifically target calcium handling and can cause electrolyte imbalances. * **B. Furosemide:** A loop diuretic that **increases** urinary calcium excretion ("Loops Lose Calcium"). It is used to treat hypercalcemia but would worsen the risk of calcium stone formation. * **C. Spironolactone:** A potassium-sparing diuretic (aldosterone antagonist). While it prevents potassium loss, it has no significant effect on renal calcium reabsorption. **NEET-PG High-Yield Pearls:** * **Mnemonic:** **L**oops **L**ose calcium; **T**hiazides **T**ake it up (reabsorb). * **Paradoxical Use:** Thiazides are also used in **Nephrogenic Diabetes Insipidus** to reduce polyuria by inducing mild volume depletion and increasing proximal water reabsorption. * **Metabolic Side Effects of Thiazides:** Hyper**G**lycemia, Hyper**L**ipidemia, Hyper**U**ricemia, and Hyper**C**alcemia (Mnemonic: **GLUC**).

Question 106: All of the following about loop diuretics are true EXCEPT:

A. Ethacrynic acid is the most ototoxic loop diuretic.
B. They release prostaglandins and lead to vasodilation.
C. Loop diuretics lead to hypokalemia and metabolic alkalosis.
D. Furosemide is the most potent loop diuretic. (Correct Answer)

Explanation: **Explanation:** **1. Why Option D is the correct (False) statement:** While Furosemide is the most commonly used loop diuretic, it is **not** the most potent. In the context of loop diuretics, potency refers to the dose required to achieve a specific effect. **Bumetanide** is the most potent loop diuretic (approximately 40 times more potent than Furosemide), followed by Torsemide. Furosemide actually has the lowest potency among the commonly used sulfonamide loop diuretics. **2. Analysis of other options:** * **Option A:** **Ethacrynic acid** is a non-sulfonamide loop diuretic. It is associated with the highest incidence of **ototoxicity** (tinnitus and deafness) compared to others and is generally reserved for patients with sulfonamide allergies. * **Option B:** Loop diuretics stimulate the intrarenal synthesis of **prostaglandins (PGE2)**. This leads to renal and systemic vasodilation, which is why IV Furosemide provides rapid symptomatic relief in acute pulmonary edema even before the diuresis begins. * **Option C:** By inhibiting the Na⁺-K⁺-2Cl⁻ symporter in the Thick Ascending Limb (TAL), more Na⁺ reaches the distal tubule. This promotes K⁺ and H⁺ secretion, leading to **hypokalemia** and **metabolic alkalosis** (contraction alkalosis). **NEET-PG High-Yield Pearls:** * **Mechanism:** Inhibits Na⁺-K⁺-2Cl⁻ cotransporter in the TAL of the Loop of Henle. * **Electrolyte Profile:** Causes "Hypo-everything" (Hypokalemia, Hypomagnesemia, Hypocalcemia, Hyponatremia) **EXCEPT** Hyperuricemia and Hyperglycemia. * **Drug of Choice:** Furosemide is the DOC for acute pulmonary edema and edema associated with CHF, cirrhosis, and renal failure. * **Torsemide:** Has a longer half-life and better oral bioavailability than Furosemide.

Question 107: Glycerol is classified as which of the following?

A. Osmotic diuretic (Correct Answer)
B. Purgative
C. Antidiabetic
D. Antiemetic

Explanation: **Explanation:** **Glycerol** is a low-molecular-weight, pharmacologically inert substance that acts as an **Osmotic Diuretic**. When administered (usually orally), it increases the osmolality of the plasma and tubular fluid. This creates an osmotic gradient that draws water out of the intracellular and interstitial compartments into the vascular space and prevents water reabsorption in the proximal convoluted tubule and descending limb of Henle's loop. **Why the other options are incorrect:** * **Purgative:** While some osmotic agents like Lactulose or Magnesium salts are used as purgatives, Glycerol's primary systemic classification in pharmacology is an osmotic agent. (Note: Glycerin suppositories can be used for constipation, but it is not its primary systemic classification). * **Antidiabetic:** Glycerol is actually a precursor for gluconeogenesis; it does not lower blood glucose. * **Antiemetic:** Glycerol has no action on the chemoreceptor trigger zone (CTZ) or the vomiting center. **High-Yield Clinical Pearls for NEET-PG:** * **Primary Use:** Glycerol is most commonly used to rapidly reduce **intraocular pressure (IOP)** in acute glaucoma and **intracranial pressure (ICP)** in cerebral edema. * **Route:** Unlike Mannitol (which must be given IV), Glycerol is **effective orally**. * **Metabolism:** Unlike Mannitol, Glycerol is metabolized in the body and provides approximately **4.3 kcal/g**, which can lead to hyperglycemia. * **Caution:** Use with extreme caution in **Diabetic patients** (due to hyperglycemia) and **Congestive Heart Failure (CHF)** patients (due to rapid expansion of extracellular fluid volume).

Question 108: Glucose transport and reabsorption in the kidneys is inhibited by which of the following?

A. Tetrodotoxin
B. GLUT
C. SGLT
D. Phlorhizin (Correct Answer)

Explanation: **Explanation:** The correct answer is **Phlorhizin**. **1. Why Phlorhizin is correct:** Glucose reabsorption in the kidney occurs primarily in the proximal convoluted tubule (PCT) via **SGLT2** (90%) and **SGLT1** (10%) transporters [1]. **Phlorhizin** is a naturally occurring glucoside (found in the bark of fruit trees) that acts as a **non-selective, competitive inhibitor of both SGLT1 and SGLT2**. By blocking these transporters, it prevents the reabsorption of filtered glucose, leading to glycosuria and a reduction in blood glucose levels. While not used clinically due to poor absorption and GI side effects, it served as the prototype for the modern "Gliflozin" class (e.g., Dapagliflozin) [2]. **2. Why other options are incorrect:** * **Tetrodotoxin:** A potent neurotoxin found in pufferfish. It acts by blocking **voltage-gated sodium channels**, inhibiting action potentials in nerve and muscle cells. It has no effect on glucose transport. * **GLUT:** These are a family of **uniporters** (facilitated diffusion) responsible for moving glucose across cell membranes (e.g., GLUT2 on the basolateral membrane of the PCT). They are the *mediators* of transport, not inhibitors. * **SGLT:** Sodium-Glucose Linked Transporters are the **targets** for inhibition. SGLT proteins facilitate the active transport of glucose; they do not inhibit it. **3. High-Yield NEET-PG Clinical Pearls:** * **SGLT2 Inhibitors (Gliflozins):** These are the clinical descendants of phlorhizin. They are now first-line agents for Type 2 Diabetes, especially in patients with **Heart Failure (HFrEF)** and **Chronic Kidney Disease (CKD)** due to their cardio-protective and reno-protective effects [2]. * **Location:** SGLT2 is located in the **S1 segment** of the PCT, while SGLT1 is in the **S3 segment**. * **Side Effects:** The most common side effect of SGLT2 inhibitors is **genital mycotic infections** (candidiasis) due to increased glucose in the urine.

Question 109: In the proximal convoluted tubule (PCT), sodium reabsorption is prevented by which class of drugs?

A. Ethacrynic acid
B. Acetazolamide
C. Osmotic diuretics (Correct Answer)
D. Triamterene

Explanation: ### Explanation **Correct Answer: C. Osmotic diuretics** **Mechanism of Action:** Osmotic diuretics (e.g., **Mannitol**) are pharmacologically inert substances that are freely filtered at the glomerulus but undergo minimal reabsorption. Their primary site of action is the **Proximal Convoluted Tubule (PCT)** and the descending limb of the Loop of Henle. By increasing the osmotic pressure of the tubular fluid, they counteract the osmotic force of sodium, thereby **preventing the passive reabsorption of water and sodium**. This leads to an increase in urine volume (diuresis) and sodium excretion (natriuresis). **Analysis of Incorrect Options:** * **A. Ethacrynic acid:** This is a **Loop diuretic**. It acts on the **Thick Ascending Limb (TAL)** of the Loop of Henle by inhibiting the $Na^+-K^+-2Cl^-$ symporter. * **B. Acetazolamide:** While it acts on the PCT, its primary mechanism is the inhibition of **Carbonic Anhydrase**. This prevents the reabsorption of **Bicarbonate ($HCO_3^-$)** rather than primarily targeting sodium reabsorption directly. * **D. Triamterene:** This is a **Potassium-sparing diuretic**. It acts on the **Late Distal Tubule and Collecting Duct** by blocking the Epithelial Sodium Channels (ENaC). **High-Yield Clinical Pearls for NEET-PG:** * **Mannitol** must be administered **intravenously**; it is not absorbed orally. * **Therapeutic Uses:** Reduction of intracranial pressure (cerebral edema) and intraocular pressure (acute glaucoma). * **Contraindications:** It is strictly contraindicated in **Acute Pulmonary Edema** and **Congestive Heart Failure** because it initially expands the extracellular fluid volume before diuresis occurs. * **Side Effect:** Can cause "Dialysis Disequilibrium Syndrome" if cleared too rapidly.

Question 110: Which of the following adverse effects is NOT caused by thiazide diuretics?

A. Hypercalcemia
B. Hypomagnesemia
C. Hypernatremia (Correct Answer)
D. Hyperuricemia

Explanation: Thiazide diuretics (e.g., Hydrochlorothiazide, Chlorthalidone) act on the **Distal Convoluted Tubule (DCT)** by inhibiting the **Na⁺-Cl⁻ symporter**. ### Why Hypernatremia is the Correct Answer Thiazides inhibit the reabsorption of Sodium (Na⁺) and Chloride (Cl⁻) in the DCT, leading to increased excretion of these ions in the urine. This loss of sodium typically results in **Hyponatremia**, not hypernatremia. In fact, thiazides are one of the most common drug-related causes of hyponatremia in clinical practice. ### Explanation of Incorrect Options (Adverse Effects of Thiazides) * **Hypercalcemia (A):** Thiazides increase Ca²⁺ reabsorption in the DCT (via the Na⁺/Ca²⁺ exchanger on the basolateral membrane). This makes them useful in treating idiopathic hypercalciuria and calcium stones. * **Hypomagnesemia (B):** Long-term use of thiazides leads to increased renal excretion of Magnesium, though the exact mechanism is less defined than that of loop diuretics. * **Hyperuricemia (D):** Thiazides compete with uric acid for the organic acid secretory secretory system in the proximal tubule, leading to decreased uric acid excretion. This can precipitate acute gouty arthritis. ### NEET-PG High-Yield Pearls: "The Hypo-Hyper Rule" To remember Thiazide side effects, think of **4 Hypos** and **4 Hypers**: * **HYPO:** Hyponatremia, Hypokalemia, Hypomagnesemia, Hypochloremic alkalosis. * **HYPER:** Hypercalcemia, Hyperuricemia, Hyperglycemia (due to decreased insulin release), Hyperlipidemia (increased LDL/Cholesterol). **Key Distinction:** Loop diuretics cause **Hypocalcemia** ("Loops lose calcium"), whereas Thiazides cause **Hypercalcemia**.

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Carbonic Anhydrase Inhibitors

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Loop Diuretics

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Thiazide and Thiazide-Like Diuretics

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Potassium-Sparing Diuretics

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Carbonic Anhydrase Inhibitors

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Osmotic Diuretics

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Combination Diuretic Therapy

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Diuretics in Heart Failure

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Diuretics in Hypertension

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Diuretics in Renal Disorders

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Adverse Effects and Drug Interactions

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Diuretics — MCQs

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