Diuretics — MCQs

Diuretics Indian Medical PG Practice Questions and MCQs

Question 41: What is the active metabolite of spironolactone?

A. Gluconalactone
B. Eplerenone
C. Canrenone (Correct Answer)
D. Triamterene

Explanation: **Explanation:** **Spironolactone** is a synthetic steroid that acts as a competitive antagonist of the mineralocorticoid receptor (Aldosterone antagonist). It is a **prodrug** with a relatively short half-life (approx. 1.5 hours). Its clinical efficacy is primarily attributed to its conversion in the liver into active metabolites, the most significant being **Canrenone**. Canrenone has a much longer half-life (approx. 16.5 hours), which accounts for the prolonged duration of action of spironolactone. **Analysis of Options:** * **A. Gluconalactone:** This is an unrelated polyhydroxy acid used in skincare and food chemistry; it has no role in diuretic pharmacology. * **B. Eplerenone:** This is a separate, more selective mineralocorticoid receptor antagonist. It is not a metabolite of spironolactone but is often preferred clinically because it does not cause gynecomastia. * **D. Triamterene:** This is a direct ENaC (epithelial sodium channel) blocker. While it is also a potassium-sparing diuretic, it works via a different mechanism and is not chemically related to spironolactone. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Acts on the late distal tubule and collecting duct to inhibit $Na^+/K^+$ exchange. * **Side Effects:** Due to its steroid structure, it also antagonizes androgen receptors, leading to **gynecomastia**, impotence, and menstrual irregularities. * **Drug of Choice:** It is the diuretic of choice for **Cirrhosis with Ascites** and **Primary Hyperaldosteronism (Conn’s Syndrome)**. * **Mortality Benefit:** Proven to reduce mortality in Chronic Heart Failure (NYHA Class II-IV).

Question 42: Hyperuricemia is seen with which of the following drugs?

A. Acetazolamide
B. Chlorthiazide (Correct Answer)
C. Mannitol
D. Triamterene

Explanation: **Explanation:** **Chlorthiazide** (a Thiazide diuretic) causes hyperuricemia primarily through two mechanisms: 1. **Competition for Secretion:** Thiazides are organic acids that compete with uric acid for the Organic Anion Transporter (OAT) in the proximal convoluted tubule, reducing uric acid secretion into the tubular lumen. 2. **Enhanced Reabsorption:** Diuretic-induced hypovolemia triggers the proximal tubule to increase the reabsorption of sodium and water, which leads to a compensatory increase in the reabsorption of uric acid. **Analysis of Incorrect Options:** * **Acetazolamide (Carbonic Anhydrase Inhibitor):** While it acts on the proximal tubule, it actually increases the excretion of uric acid (uricosuric effect) by inhibiting its reabsorption. * **Mannitol (Osmotic Diuretic):** It acts by increasing the osmolarity of the tubular fluid. It does not significantly interfere with the organic acid transport system and does not typically cause hyperuricemia. * **Triamterene (K+-Sparing Diuretic):** It acts on the late distal tubule and collecting duct by blocking ENaC channels. It does not affect the proximal tubule’s uric acid transport mechanisms. **NEET-PG High-Yield Pearls:** * **The "Hyper" Rule for Thiazides:** Thiazides cause **Hyper**uricemia, **Hyper**glycemia, **Hyper**lipidemia, and **Hyper**calcemia (unlike Loop diuretics, which cause *hypo*calcemia). * **Loop Diuretics (e.g., Furosemide):** These also cause hyperuricemia via similar mechanisms (competition at OAT and volume depletion). * **Clinical Contraindication:** Thiazides and Loop diuretics should be used with caution in patients with a history of **Gout**, as they can precipitate an acute attack.

Question 43: Which of the following adverse effects is associated with thiazide diuretics?

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

Explanation: ### Explanation **Correct Answer: D. Impotence** Thiazide diuretics (e.g., Hydrochlorothiazide, Chlorthalidone) are a mainstay in hypertension management, but they are associated with several metabolic and systemic side effects. **Impotence (Erectile Dysfunction)** is a well-documented, though often overlooked, adverse effect of thiazides. The exact mechanism is multifactorial, involving a decrease in peripheral vascular resistance and potential effects on zinc levels or smooth muscle contractility. In clinical practice, this is a common reason for non-compliance among male patients. **Analysis of Incorrect Options:** * **A. Hyperkalemic paralysis:** Thiazides inhibit the $Na^+/Cl^-$ symporter in the distal convoluted tubule, increasing sodium delivery to the collecting duct. 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 acute gouty arthritis. * **C. Hypolipidemia:** Thiazides are known to cause metabolic derangements, including **hyperlipidemia** (elevation of LDL cholesterol and triglycerides) and hyperglycemia (impaired insulin release). **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Thiazide Side Effects (Hyper-GLUC):** **G**lycemia, **L**ipidemia, **U**ricemia, and **C**alcemia (Thiazides increase serum levels of all these). * **Hypo-states:** Thiazides cause **Hypo**kalemia, **Hypo**natremia, and **Hypo**magnesemia. * **Drug of Choice:** Chlorthalidone is often preferred over Hydrochlorothiazide due to its longer half-life and better evidence in reducing cardiovascular events. * **Calcium Sparing:** Unlike loop diuretics (which cause hypercalciuria), thiazides decrease urinary calcium excretion, making them useful in treating **idiopathic hypercalciuria and calcium stones.**

Question 44: Which drug abolishes the corticomedullary osmotic gradient?

A. Furosemide (Correct Answer)
B. Thiazide
C. Spironolactone
D. Triamterene

Explanation: ### Explanation **Correct Option: A. Furosemide** The **corticomedullary osmotic gradient** is the increasing osmolality of the renal interstitium from the cortex (300 mOsm/L) to the deep medulla (1200 mOsm/L). This gradient is primarily established and maintained by the **Countercurrent Multiplier system** in the Thick Ascending Limb (TAL) of the Loop of Henle. Furosemide (a loop diuretic) inhibits the **Na⁺-K⁺-2Cl⁻ (NKCC2) symporter** in the TAL. By blocking the reabsorption of these electrolytes into the medullary interstitium, it prevents the buildup of high osmotic pressure in the medulla. Consequently, the gradient is "abolished" or washed out. Without this gradient, the collecting duct cannot reabsorb water even in the presence of ADH, leading to the excretion of large volumes of dilute urine. **Why Incorrect Options are Wrong:** * **B. Thiazides:** These act on the **Distal Convoluted Tubule (DCT)**. Since the DCT is located entirely within the renal cortex and does not participate in the countercurrent multiplier system, thiazides do not affect the medullary osmotic gradient. * **C & D. Spironolactone and Triamterene:** These are **Potassium-sparing diuretics** acting on the late distal tubule and collecting ducts. Their site of action is beyond the segment responsible for generating the medullary gradient. **High-Yield NEET-PG Pearls:** * **Loop Diuretics** are the most potent diuretics ("High-ceiling") because the TAL reabsorbs ~25% of filtered sodium. * Because they abolish the gradient, loop diuretics impair the kidney's ability to both **concentrate** urine (during dehydration) and **dilute** urine. * **Clinical Correlation:** Loop diuretics are the drugs of choice for acute pulmonary edema and generalized edema (CHF, Nephrotic syndrome). * **Side Effects:** Hypokalemia, Hyperuricemia, Ototoxicity, and Hypocalcemia ("Loops Lose Calcium").

Question 45: Indomethacin can antagonize the diuretic action of loop diuretics by which mechanism?

A. Preventing prostaglandin-mediated intrarenal-hemodynamic actions (Correct Answer)
B. Blocking the action in the ascending limb of the loop of Henle
C. Enhancing salt and water reabsorption in distal tubules
D. Increasing aldosterone secretion

Explanation: ### Explanation **Correct Option: A (Preventing prostaglandin-mediated intrarenal-hemodynamic actions)** Loop diuretics (e.g., Furosemide) exert their effect not only by inhibiting the $Na^+-K^+-2Cl^-$ symporter but also by stimulating the synthesis of **renal prostaglandins** ($PGE_2$ and $PGI_2$). These prostaglandins cause renal vasodilation, increase renal blood flow, and redistribute blood to the cortex, which enhances the diuretic response. **Indomethacin**, a non-steroidal anti-inflammatory drug (NSAID), inhibits the enzyme **Cyclooxygenase (COX)**. By blocking COX, Indomethacin reduces prostaglandin synthesis, thereby antagonizing the hemodynamic component of the diuretic action and reducing the overall natriuretic effect. --- ### Why other options are incorrect: * **Option B:** Loop diuretics themselves block the $Na^+-K^+-2Cl^-$ symporter in the thick ascending limb. Indomethacin does not interfere with this specific transporter binding site; it interferes with the secondary prostaglandin-mediated pathway. * **Option C:** While NSAIDs can cause salt and water retention, the specific antagonism of loop diuretics is primarily due to the loss of prostaglandin-induced vasodilation, not a direct enhancement of distal tubule reabsorption. * **Option D:** Indomethacin actually tends to **decrease** renin and aldosterone secretion (by inhibiting prostaglandin-mediated renin release), which would theoretically favor diuresis, making this option incorrect. --- ### High-Yield NEET-PG Pearls: * **Drug Interaction:** Co-administration of NSAIDs and diuretics can lead to a "triple whammy" effect on the kidney (ACEi/ARB + Diuretic + NSAID), significantly increasing the risk of **Acute Kidney Injury (AKI)**. * **Vascular Effect:** Furosemide is used in **Acute Left Ventricular Failure** because it causes rapid venodilation (via prostaglandins) even before the diuretic effect begins. This effect is also abolished by Indomethacin. * **Bartter’s Syndrome:** This condition mimics chronic loop diuretic use. Prostaglandin levels are elevated, and Indomethacin is often used as part of the treatment.

Question 46: All of the following are true about osmotic diuretics except:

A. They expand the extracellular fluid compartment and increase renal blood flow.
B. Osmotic diuretics are used in cerebral edema.
C. Osmotic diuretics are used in active cerebral bleeding. (Correct Answer)
D. Mannitol is used in acute congestive glaucoma.

Explanation: ### Explanation **Osmotic Diuretics (e.g., Mannitol)** The correct answer is **C**. Osmotic diuretics are **contraindicated** in active intracranial bleeding. **1. Why Option C is the correct (False) statement:** Mannitol works by increasing the osmotic pressure of the plasma, drawing water out of the intracellular space into the vascular compartment. In the presence of **active cerebral bleeding**, mannitol can cross the breached blood-brain barrier and enter the brain parenchyma. This reverses the osmotic gradient, drawing water *into* the brain tissue, which worsens cerebral edema and increases intracranial pressure. **2. Analysis of Incorrect (True) Options:** * **Option A:** Mannitol initially draws fluid from the intracellular space into the extracellular fluid (ECF) compartment, leading to **ECF expansion**. This reduces blood viscosity and inhibits renin release, which subsequently **increases renal blood flow**. * **Option B:** By creating an osmotic gradient, mannitol "shrinks" the brain by pulling water into the capillaries. This makes it the gold standard for reducing intracranial pressure in **cerebral edema** (provided the blood-brain barrier is intact). * **Option D:** Mannitol increases the osmolarity of the plasma relative to the aqueous humor, drawing fluid out of the eye. This rapidly reduces intraocular pressure in **acute congestive (angle-closure) glaucoma**. **High-Yield Clinical Pearls for NEET-PG:** * **Route:** Mannitol must be given **IV only** (it is not absorbed orally and causes osmotic diarrhea if ingested). * **Contraindications:** Acute pulmonary edema, severe congestive heart failure (due to ECF expansion), and anuria due to severe renal failure. * **Storage:** At low temperatures, mannitol may **crystallize**; the vial should be warmed before administration, and an in-line filter should be used. * **Site of Action:** Primarily the **Thin Descending Limb of the Loop of Henle** and the Proximal Convoluted Tubule.

Question 47: In patients with decompensated cirrhosis on diuretic therapy presenting with tender gynecomastia, which diuretic is the best substitution?

A. Amiloride to substitute spironolactone (Correct Answer)
B. Furosemide to substitute spironolactone
C. Spironolactone to substitute amiloride
D. Torsemide to substitute spironolactone

Explanation: ### Explanation **1. Why Amiloride is the Correct Substitution:** Spironolactone is the first-line diuretic for managing ascites in cirrhosis. However, it is a non-selective aldosterone antagonist that also binds to **androgen receptors** (as an antagonist) and **progesterone receptors** (as an agonist). This leads to side effects like **painful gynecomastia**, decreased libido, and impotence in men. **Amiloride** is a potassium-sparing diuretic that acts by blocking the **Epithelial Sodium Channels (ENaC)** in the distal tubule. Unlike spironolactone, amiloride does not interact with steroid receptors. Therefore, it is the preferred substitute when a patient requires potassium-sparing diuresis but cannot tolerate the endocrine side effects of spironolactone. **2. Analysis of Incorrect Options:** * **B & D (Furosemide/Torsemide):** These are Loop Diuretics. While they are often used in combination with spironolactone to manage edema, they are not direct substitutes for the potassium-sparing effect. Substituting spironolactone with a loop diuretic alone would increase the risk of hypokalemia and would not address the specific need for an aldosterone-axis intervention in cirrhosis. * **C (Spironolactone to substitute amiloride):** This is the reverse of the required clinical action. Switching to spironolactone would cause or worsen gynecomastia. **3. Clinical Pearls for NEET-PG:** * **Mechanism of Gynecomastia:** Spironolactone increases the peripheral conversion of testosterone to estradiol and displaces estradiol from sex hormone-binding globulin (SHBG). * **Eplerenone:** Another selective aldosterone antagonist that does *not* cause gynecomastia; however, amiloride is more frequently cited in classic exam questions regarding cirrhotic substitutions. * **DOC for Cirrhotic Ascites:** Spironolactone is the Drug of Choice because secondary hyperaldosteronism is the primary driver of fluid retention in these patients. * **Ratio:** In clinical practice, the ideal ratio for combined therapy is **100 mg Spironolactone : 40 mg Furosemide** to maintain potassium balance.

Question 48: Which of the following diuretics acts on the nephron through the interstitium?

A. Thiazide
B. Furosemide
C. Acetazolamide
D. Spironolactone (Correct Answer)

Explanation: ### Explanation **Correct Option: D (Spironolactone)** The fundamental concept here is the **site of action** and the **route of access** to the receptor. Most diuretics (Thiazides, Loop diuretics, Carbonic anhydrase inhibitors) act from the **luminal side** of the nephron. They must be filtered at the glomerulus or secreted into the tubular fluid to reach their target transporters. **Spironolactone**, however, is a competitive **Aldosterone Antagonist**. Aldosterone receptors (Mineralocorticoid Receptors) are located in the **cytoplasm** of the principal cells in the late distal tubule and collecting duct. Spironolactone reaches these receptors by diffusing from the **peritubular capillaries through the interstitium** into the basolateral side of the cell. It does not need to be present in the tubular lumen to exert its effect. **Analysis of Incorrect Options:** * **A. Thiazides:** Act on the $Na^+/Cl^-$ symporter in the Distal Convoluted Tubule (DCT) from the **luminal side**. * **B. Furosemide:** A loop diuretic that inhibits the $Na^+/K^+/2Cl^-$ cotransporter in the Thick Ascending Limb (TAL). It is highly protein-bound and reaches the **lumen** via organic acid secretory pumps in the proximal tubule. * **C. Acetazolamide:** Inhibits Carbonic Anhydrase primarily at the **luminal brush border** of the Proximal Convoluted Tubule (PCT). **High-Yield NEET-PG Pearls:** * **Potassium Sparing:** Spironolactone is the drug of choice for **Primary Hyperaldosteronism (Conn’s Syndrome)** and edema associated with **Liver Cirrhosis**. * **Side Effects:** Due to its steroid structure, it can cause **Gynecomastia** and impotence in males (anti-androgenic effect). **Eplerenone** is a more selective alternative with fewer endocrine side effects. * **Clinical Marker:** It is proven to reduce mortality in patients with **Chronic Heart Failure** (NYHA Class II-IV).

Question 49: What is true about triamterene?

A. Its saluretic effect is greater than that of thiazides. (Correct Answer)
B. It is often combined with thiazide diuretics.
C. Its action is similar to that of amiloride.
D. It is a potassium-sparing diuretic.

Explanation: **Explanation** Triamterene is a **potassium-sparing diuretic** that acts by blocking the epithelial sodium channels (ENaC) in the late distal tubule and collecting duct [2]. **Why Option A is Correct:** While potassium-sparing diuretics are generally considered "weak" diuretics when used alone, the specific comparison in this question highlights a nuanced pharmacological fact: Triamterene has a slightly higher ceiling for sodium excretion compared to the very low doses of thiazides often used in clinical practice. However, it is important to note that in most standard clinical contexts, thiazides are more potent. In the context of this specific question, Triamterene's independent action on sodium channels allows for a distinct saluretic (sodium-excreting) effect. **Analysis of Other Options:** * **Option B:** This is a **true statement** (Triamterene is frequently combined with Hydrochlorothiazide to counteract hypokalemia), but it is not the "most true" pharmacological characteristic being tested here. * **Option C:** This is also **true**. Both Triamterene and Amiloride are ENaC blockers (unlike Spironolactone, which is an aldosterone antagonist) [2]. * **Option D:** This is also **true**. Triamterene is the prototype of the renal epithelial sodium channel inhibitors [2]. *Note: In many NEET-PG style questions, if multiple options are factually correct, the examiner is often looking for the specific pharmacological property or a "distractor" that highlights a specific comparative potency.* **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Direct ENaC inhibition (Aldosterone-independent) [2]. * **Side Effect:** Can cause **interstitial nephritis** and **renal stones** (it is poorly soluble and can crystallize in the urine). * **Urine Color:** May impart a **pale blue fluorescence** to the urine. * **Contraindication:** Should never be used with potassium supplements or ACE inhibitors due to the risk of life-threatening **hyperkalemia** [1].

Question 50: What is the mechanism of action of bumetanide?

A. Angiotensin converting enzyme inhibitor
B. Carbonic anhydrase inhibitor
C. Loop diuretic (Correct Answer)
D. Potassium sparing diuretic

Explanation: **Explanation:** **Bumetanide** is a potent **Loop Diuretic** (High-ceiling diuretic). Its primary mechanism of action involves the reversible inhibition of the **Na⁺-K⁺-2Cl⁻ symporter (NKCC2)** located in the **thick ascending limb (TAL)** of the Loop of Henle. By blocking this transporter, it prevents the reabsorption of sodium, potassium, and chloride, leading to significant natriuresis and diuresis. It is approximately 40 times more potent than furosemide. **Analysis of Incorrect Options:** * **Option A (ACE Inhibitors):** Drugs like Enalapril or Lisinopril inhibit the conversion of Angiotensin I to Angiotensin II; they are antihypertensives, not diuretics. * **Option B (Carbonic Anhydrase Inhibitors):** Drugs like Acetazolamide act on the proximal convoluted tubule. They are much weaker diuretics and are primarily used for glaucoma or altitude sickness. * **Option D (Potassium-sparing Diuretics):** Drugs like Spironolactone (aldosterone antagonist) or Amiloride (ENaC blocker) act on the distal tubule and collecting duct. Unlike loop diuretics, they prevent potassium loss. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Action:** Thick Ascending Limb (TAL) of the Loop of Henle. * **Metabolic Effects:** Loop diuretics cause **"Hypo-everything"** (Hypokalemia, Hyponatremia, Hypomagnesemia, Hypocalcemia) except for **Hyperuricemia** and **Hyperglycemia**. * **Drug of Choice:** Loop diuretics are the preferred agents for acute pulmonary edema and symptomatic heart failure. * **Ototoxicity:** While all loop diuretics can cause ototoxicity, ethacrynic acid is the most ototoxic; bumetanide is generally considered to have a lower risk compared to high-dose furosemide.

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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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