Diuretics — MCQs

Diuretics Indian Medical PG Practice Questions and MCQs

Question 11: Thiazides cause all the following side-effects except-

A. Hypercalcemia
B. Hypokalemia
C. Metabolic acidosis (Correct Answer)
D. Metabolic alkalosis

Explanation: **Explanation:** Thiazide diuretics act on the **Distal Convoluted Tubule (DCT)** by inhibiting the $Na^+/Cl^-$ symporter. This mechanism leads to a specific pattern of electrolyte and acid-base disturbances. **Why Metabolic Acidosis is the correct answer:** Thiazides do **not** cause metabolic acidosis; instead, they cause **Metabolic Alkalosis**. By increasing sodium delivery to the collecting ducts, they stimulate the exchange of $Na^+$ for $H^+$ and $K^+$. The loss of $H^+$ ions in the urine leads to an increase in serum bicarbonate levels (contraction alkalosis). In contrast, metabolic acidosis is a side effect of Carbonic Anhydrase inhibitors (like Acetazolamide) or Potassium-sparing diuretics. **Analysis of Incorrect Options:** * **Hypercalcemia:** Thiazides increase calcium reabsorption in the DCT (unlike loop diuretics which cause hypocalcemia). This makes them useful in treating idiopathic hypercalciuria and calcium stones. * **Hypokalemia:** Increased sodium delivery to the late distal tubule promotes $K^+$ secretion into the lumen, leading to potassium depletion. * **Metabolic Alkalosis:** As explained above, the loss of $H^+$ and $Cl^-$ ions results in an alkalotic state. **High-Yield Clinical Pearls for NEET-PG:** * **The "Hyper" Mnemonic:** Thiazides cause **Hyper**glycemia, **Hyper**uricemia (can precipitate Gout), **Hyper**lipidemia, and **Hyper**calcemia. * **The "Hypo" Mnemonic:** They cause **Hypo**kalemia, **Hypo**natremia, and **Hypo**magnesemia. * **Drug of Choice:** Thiazides are the first-line treatment for Hypertension in patients with Osteoporosis due to their calcium-sparing effect.

Question 12: Which of the following diuretics should not be administered along with aminoglycosides?

A. Chlorthiazide
B. Furosemide (Correct Answer)
C. Dorzolamide
D. Canrenone

Explanation: **Explanation:** The correct answer is **Furosemide**. **1. Why Furosemide is the correct answer:** Furosemide is a potent **Loop Diuretic** that inhibits the $Na^+-K^+-2Cl^-$ symporter in the thick ascending limb of the Loop of Henle. A significant adverse effect of loop diuretics is **ototoxicity** (damage to the inner ear), which can manifest as tinnitus, hearing loss, or vertigo. **Aminoglycosides** (e.g., Gentamicin, Amikacin) are also notoriously ototoxic. When administered together, they exert a **synergistic toxic effect**, significantly increasing the risk of permanent deafness. This interaction is a classic contraindication in clinical practice. **2. Why the other options are incorrect:** * **A. Chlorthiazide:** This is a Thiazide diuretic. While thiazides can cause metabolic disturbances (hypokalemia, hyperuricemia), they are not typically associated with ototoxicity and do not potentiate aminoglycoside-induced ear damage. * **C. Dorzolamide:** This is a topical Carbonic Anhydrase Inhibitor used primarily in glaucoma to reduce intraocular pressure. It lacks the systemic profile to interact with aminoglycosides in this manner. * **D. Canrenone:** This is an active metabolite of Spironolactone (a Potassium-sparing diuretic). Its primary side effects are related to hyperkalemia and hormonal changes (gynecomastia), not ototoxicity. **3. NEET-PG High-Yield Pearls:** * **Ototoxic Loop Diuretics:** Ethacrynic acid is the *most* ototoxic, while Furosemide is the most commonly implicated clinically. * **Mechanism of Ototoxicity:** Loop diuretics alter the electrolyte composition of the endolymph by affecting ion transporters in the *stria vascularis* of the cochlea. * **Other Synergistic Interactions:** Avoid combining aminoglycosides with other ototoxic/nephrotoxic drugs like **Cisplatin**, **Vancomycin**, or **Amphotericin B**. * **Canrenone Fact:** It is the major active metabolite responsible for the diuretic action of Spironolactone.

Question 13: Spironolactone is used in the treatment of patients with Conn's syndrome. Which of the following is the most important adverse reaction of spironolactone therapy?

A. Antiandrogen effects (Correct Answer)
B. Cardiac arrhythmia
C. Dehydration
D. Hyperkalemia

Explanation: **Explanation:** Spironolactone is a potassium-sparing diuretic that acts as a competitive antagonist at the mineralocorticoid receptor. In **Conn’s syndrome** (primary hyperaldosteronism), it is used to counteract the effects of excess aldosterone. **Why Antiandrogen effects is the correct answer:** While spironolactone is a mineralocorticoid antagonist, it is **non-selective**. It also acts as a potent antagonist at **androgen receptors** and inhibits steroidogenesis (decreasing testosterone synthesis). In clinical practice, these hormonal side effects are the most bothersome and "important" reasons for treatment non-compliance. In males, this manifests as **gynecomastia** and impotence; in females, it causes **menstrual irregularities** and breast tenderness. **Analysis of Incorrect Options:** * **Hyperkalemia (D):** While hyperkalemia is a common and potentially dangerous side effect of all potassium-sparing diuretics, the question asks for the most *characteristic* adverse reaction associated with spironolactone's unique chemical structure. In the context of NEET-PG, "antiandrogen effects" is the classic "distinguishing" side effect tested for spironolactone. * **Cardiac arrhythmia (B):** This is a secondary consequence of severe hyperkalemia, not a direct effect of the drug itself. * **Dehydration (C):** Spironolactone is a relatively weak diuretic; significant dehydration is rare compared to loop diuretics like furosemide. **High-Yield Clinical Pearls for NEET-PG:** * **Eplerenone:** A selective aldosterone antagonist that does **not** have antiandrogenic side effects (no gynecomastia). It is the preferred alternative if spironolactone is not tolerated. * **Drug of Choice:** Spironolactone is the drug of choice for **Conn’s syndrome** and **Ascites in Liver Cirrhosis**. * **Mortality Benefit:** It is proven to reduce mortality in Congestive Heart Failure (NYHA Class III/IV). * **Other uses:** Due to its antiandrogenic properties, it is also used to treat **Hirsutism** and **Acne** in females.

Question 14: What are the diuretics of choice for acute pulmonary edema?

A. Loop diuretics (Correct Answer)
B. Thiazides
C. Spironolactone
D. Mannitol

Explanation: **Explanation:** **1. Why Loop Diuretics are the Correct Answer:** Loop diuretics (specifically **Furosemide**) are the drugs of choice for acute pulmonary edema due to their unique **dual mechanism of action**: * **Immediate Vasodilatory Effect:** When given intravenously, they cause rapid venodilation (mediated by prostaglandin release) even before the onset of diuresis. This increases venous capacitance, reduces venous return (preload), and provides immediate relief from pulmonary congestion. * **Potent Diuresis:** By inhibiting the **Na⁺-K⁺-2Cl⁻ symporter** in the Thick Ascending Limb of Henle, they induce massive diuresis, reducing total body fluid volume and further alleviating pulmonary edema. **2. Why Other Options are Incorrect:** * **Thiazides:** These are "low ceiling" diuretics with moderate efficacy. They act on the distal tubule and lack the rapid vasodilatory properties required for an acute emergency. * **Spironolactone:** This is a potassium-sparing diuretic (aldosterone antagonist). It has a slow onset of action (taking days to work) and is used for long-term remodeling in heart failure, not acute stabilization. * **Mannitol:** As an osmotic diuretic, it initially increases extracellular fluid volume before diuresis occurs. This can acutely worsen pulmonary edema and precipitate heart failure. **3. High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** IV Furosemide (Lasix). * **Ototoxicity:** A key side effect of loop diuretics, especially when used with aminoglycosides. Ethacrynic acid is the most ototoxic. * **Electrolyte Profile:** Loop diuretics cause "Hypo-Everything" (Hypokalemia, Hypomagnesemia, Hypocalcemia), except for **Hyperuricemia** and **Hyperglycemia**. * **Sulfa Allergy:** Most loop diuretics are sulfonamide derivatives; **Ethacrynic acid** is the alternative for patients with sulfa allergies.

Question 15: A 32-year-old male patient is treated for hypertension with thiazides. Which of the following adverse effects can occur in this patient?

A. Hyperkalemic paralysis
B. Hypouricemia
C. Hypolipidemia
D. Impotence (Correct Answer)

Explanation: **Explanation:** Thiazide diuretics (e.g., Hydrochlorothiazide, Chlorthalidone) are first-line antihypertensive agents, but they are associated with several metabolic and systemic side effects. **Why Impotence is Correct:** Sexual dysfunction, specifically **erectile dysfunction (impotence)**, is a well-documented side effect of thiazide diuretics. While the exact mechanism is multifactorial, it is thought to involve a decrease in peripheral vascular resistance and a reduction in zinc levels, which is essential for testosterone production. In clinical trials, thiazides are more frequently associated with impotence compared to other antihypertensives like ACE inhibitors or Calcium Channel Blockers. **Analysis of Incorrect Options:** * **A. Hyperkalemic paralysis:** Thiazides inhibit the $Na^+/Cl^-$ symporter in the distal convoluted tubule, increasing sodium delivery to the collecting ducts. This promotes potassium excretion, leading to **hypokalemia**, not hyperkalemia. * **B. Hypouricemia:** Thiazides compete with uric acid for the organic acid secretory secretory pump in the proximal tubule. This leads to decreased uric acid excretion, resulting in **hyperuricemia**, which can precipitate gout. * **C. Hypolipidemia:** Thiazides can cause a transient increase in serum cholesterol and LDL levels (**hyperlipidemia**), though this effect often diminishes with long-term therapy. **High-Yield Clinical Pearls for NEET-PG:** * **The "Hyper" Rule:** Thiazides cause **Hyper**glycemia, **Hyper**uricemia, **Hyper**lipidemia, and **Hyper**calcemia (useful in treating idiopathic hypercalciuria/kidney stones). * **The "Hypo" Rule:** Thiazides cause **Hypo**kalemia, **Hypo**natremia, and **Hypo**magnesemia. * **Chlorthalidone** is currently preferred over Hydrochlorothiazide due to its longer half-life and superior evidence in reducing cardiovascular events.

Question 16: Which of the following diuretics decreases renal lithium clearance?

A. acetazolamide
B. hydrochlorothiazide (Correct Answer)
C. furosemide
D. spironolactone

Explanation: **Explanation:** The correct answer is **hydrochlorothiazide**. **Mechanism of Interaction:** Lithium is handled by the kidneys in a manner very similar to sodium. Approximately 80% of filtered lithium is reabsorbed in the proximal convoluted tubule (PCT). **Thiazide diuretics** (like hydrochlorothiazide) inhibit the Na+/Cl- symporter in the distal tubule, leading to increased excretion of sodium and water. This induces a state of mild volume depletion. In response, the proximal tubule compensatorily increases the reabsorption of sodium and water to maintain blood volume. Because the PCT cannot distinguish between sodium and lithium ions, it also increases the **proximal reabsorption of lithium**. This significantly decreases renal lithium clearance, leading to toxic serum lithium levels. **Analysis of Incorrect Options:** * **Acetazolamide:** This carbonic anhydrase inhibitor actually *increases* lithium excretion. By inhibiting bicarbonate reabsorption in the PCT, it also inhibits the co-transport of lithium, potentially lowering serum levels. * **Furosemide:** Loop diuretics act on the thick ascending limb of Henle. While they can affect lithium levels, the effect is much less consistent and less clinically significant than thiazides because they do not trigger the same degree of compensatory proximal reabsorption. * **Spironolactone:** This potassium-sparing diuretic acts on the collecting duct. It generally has a negligible effect on lithium clearance compared to thiazides. **Clinical Pearls for NEET-PG:** * **Drug of Choice for Lithium-Induced Diabetes Insipidus:** Amiloride (it blocks the ENaC channels in the collecting duct, preventing lithium from entering the cells). * **Drugs that increase Lithium levels:** Thiazides, NSAIDs (except aspirin/sulindac), and ACE inhibitors/ARBs. * **Lithium Toxicity:** Characterized by coarse tremors, ataxia, seizures, and nephrogenic diabetes insipidus.

Question 17: Which of the following diuretics keeps urine isotonic?

A. Thiazide diuretics
B. Loop diuretics (Correct Answer)
C. Carbonic anhydrase inhibitors
D. None of the above

Explanation: **Explanation:** The correct answer is **Loop Diuretics** (e.g., Furosemide). This occurs because loop diuretics inhibit the **Na⁺-K⁺-2Cl⁻ symporter** in the Thick Ascending Limb (TAL) of the Loop of Henle. **Why Loop Diuretics keep urine isotonic:** The TAL is responsible for reabsorbing solutes without water, which creates the **medullary osmotic gradient**. This gradient is essential for both concentrating urine (via ADH) and diluting urine. By blocking solute reabsorption in this segment, loop diuretics abolish the medullary hypertonicity. Consequently, the kidney loses its ability to concentrate or dilute urine, resulting in the excretion of urine that has the same osmolality as plasma (~300 mOsm/L), a phenomenon known as **isosthenuria**. **Why other options are incorrect:** * **Thiazide Diuretics:** These act on the Distal Convoluted Tubule (DCT). They interfere with the kidney’s ability to dilute urine but do **not** affect the medullary gradient. Therefore, the urine remains concentrated (hypertonic) relative to the initial filtrate. * **Carbonic Anhydrase Inhibitors:** These act on the Proximal Convoluted Tubule. While they increase bicarbonate and sodium excretion, they do not disrupt the primary concentrating mechanism of the medulla, thus not resulting in strictly isotonic urine. **High-Yield Clinical Pearls for NEET-PG:** * **"High Ceiling" Diuretics:** Loop diuretics are called this because they have a dose-dependent response with a very high maximal efficacy. * **Calcium Effect:** Loop diuretics cause **hypocalcemia** ("Loops Lose Calcium"), whereas Thiazides cause **hypercalcemia**. * **Drug of Choice:** Loop diuretics are the DOC for acute pulmonary edema and generalized edema (CHF, Nephrotic syndrome).

Question 18: What is the primary site of action for Chlorthalidone?

A. Early distal tubule (Correct Answer)
B. Late distal tubule
C. Collecting duct (medullary portion)
D. Collecting duct (cortical portion)

Explanation: **Explanation:** **Chlorthalidone** is a thiazide-like diuretic. Although it differs chemically from benzothiadiazines, it shares the same mechanism of action and site of action as thiazide diuretics. **1. Why Option A is Correct:** The primary site of action for Chlorthalidone (and all thiazides) is the **early distal convoluted tubule (DCT)**. It works by inhibiting the **Na⁺-Cl⁻ symporter** on the luminal membrane. By blocking this transporter, it increases the excretion of sodium and chloride, leading to diuresis. **2. Why the Other Options are Incorrect:** * **Option B (Late distal tubule) & Option D (Cortical collecting duct):** These are the sites of action for **Potassium-sparing diuretics** (e.g., Spironolactone, Amiloride). These segments are regulated by Aldosterone and involve the ENaC (Epithelial Sodium Channels). * **Option C (Medullary collecting duct):** This is the site where **Vasopressin (ADH)** acts via V2 receptors to regulate water reabsorption through aquaporins. Diuretics do not primarily target this segment. **Clinical Pearls for NEET-PG:** * **Potency & Duration:** Chlorthalidone is significantly more potent and has a much **longer half-life (~40–60 hours)** than Hydrochlorothiazide, making it the preferred agent for hypertension management according to many guidelines. * **Metabolic Side Effects:** Remember the mnemonic **"Hyper GLUC"**—Thiazides cause Hyper**G**lycemia, Hyper**L**ipidemia, Hyper**U**ricemia, and Hyper**C**alcemia. * **Paradoxical Use:** Despite being a diuretic, it is used to treat **Nephrogenic Diabetes Insipidus** because it induces mild hypovolemia, which increases proximal tubular reabsorption of salt and water. * **Inefficacy:** Thiazides generally lose efficacy when the GFR falls below **30 mL/min** (except for Metolazone).

Question 19: What is the longest-acting thiazide diuretic?

A. Chlorthiazide
B. Chlorthalidone (Correct Answer)
C. Indapamide
D. Metolazone

Explanation: **Chlorthalidone** is the longest-acting diuretic among the options provided [1]. Although it is chemically a "thiazide-like" diuretic (lacking the benzothiadiazine ring) [2, 3], it shares the same mechanism of action: inhibiting the **Na⁺-Cl⁻ symporter** in the Distal Convoluted Tubule (DCT) [1, 2].**Why Chlorthalidone is the correct answer:**The prolonged duration of action of Chlorthalidone (**48–72 hours**) [2] is primarily due to its high affinity for **carbonic anhydrase** in erythrocytes. This leads to extensive binding within red blood cells, creating a large reservoir that is slowly released into the plasma and delivered to the kidneys. Because of this long half-life, it provides superior 24-hour blood pressure control compared to Hydrochlorothiazide [1].**Analysis of Incorrect Options:** * **A. Chlorthiazide:** This is the prototype thiazide but has a very short half-life (approx. 1.5–2 hours) and low lipid solubility [2]. * **C. Indapamide:** A thiazide-like diuretic with a duration of action of about 24 hours [2, 3]. It is notable for its dual action (diuretic + vasodilation) and is often preferred in patients with renal impairment. * **D. Metolazone:** A potent thiazide-like diuretic with a duration of action of about 12–24 hours [2, 3]. It is unique because it remains effective even when the GFR is low (<30 mL/min).**High-Yield Clinical Pearls for NEET-PG:** * **Potency:** Chlorthalidone is roughly 1.5 to 2 times more potent than Hydrochlorothiazide. * **Drug of Choice:** Recent hypertension guidelines (like ACC/AHA) often prefer Chlorthalidone over other thiazides due to its proven reduction in cardiovascular events. * **Metabolic Side Effects:** All thiazides can cause the "Hyper" states: **Hyper**glycemia, **Hyper**lipidemia, **Hyper**uricemia, and **Hyper**calcemia; and "Hypo" states: **Hypo**kalemia, **Hypo**natremia, and **Hypo**magnesemia.

Question 20: Which of the following diuretics will continue to induce significant diuresis after return of blood volume to normal levels?

A. hydrochlorothiazide
B. spironolactone
C. triamterene
D. furosemide (Correct Answer)

Explanation: **Explanation:** The correct answer is **furosemide**. The primary reason lies in the **potency and site of action** of Loop diuretics compared to other classes. **1. Why Furosemide is Correct:** Furosemide is a "High-Ceiling" diuretic that inhibits the **Na⁺-K⁺-2Cl⁻ cotransporter (NKCC2)** in the Thick Ascending Limb (TAL) of the Loop of Henle. This segment is responsible for reabsorbing approximately 25% of filtered sodium. Unlike Thiazides or Potassium-sparing diuretics, Loop diuretics have a massive diuretic capacity that is relatively independent of the body's fluid status. Even after blood volume returns to normal, furosemide continues to exert a powerful effect because the TAL has a high reabsorptive capacity that, when blocked, results in significant solute and water loss. **2. Why Other Options are Incorrect:** * **Hydrochlorothiazide (A):** This is a "Low-Ceiling" diuretic acting on the Distal Convoluted Tubule (DCT), where only 5-10% of sodium is reabsorbed. Its efficacy is limited; once the initial fluid excess is removed, the compensatory activation of the Renin-Angiotensin-Aldosterone System (RAAS) easily offsets its mild diuretic effect. * **Spironolactone (B) & Triamterene (C):** These are weak, potassium-sparing diuretics acting on the collecting duct (reabsorbing <3% sodium). Their effect is too minimal to induce "significant" diuresis once normovolemia is achieved, as they are primarily used to counteract potassium loss or in specific hyperaldosteronic states. **Clinical Pearls for NEET-PG:** * **Braking Phenomenon:** Continued use of loop diuretics leads to hypertrophy of distal segments, which eventually limits their effect (compensated by adding a Thiazide). * **Drug of Choice:** Furosemide is the drug of choice for **Acute Pulmonary Edema** due to its rapid action and additional venodilatory effect (mediated by Prostaglandins). * **Ototoxicity:** Furosemide can cause dose-dependent hearing loss, especially when combined with Aminoglycosides.

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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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