Diuretics — MCQs

Diuretics Indian Medical PG Practice Questions and MCQs

Question 31: Which drug is used in the treatment of idiopathic hypercalciuria?

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

Explanation: ### Explanation **Correct Option: D (Thiazide)** Thiazide diuretics (e.g., Hydrochlorothiazide, Chlorthalidone) are the drugs of choice for idiopathic hypercalciuria. * **Mechanism:** Thiazides inhibit the $Na^+/Cl^-$ symporter in the Distal Convoluted Tubule (DCT). This decrease in intracellular sodium enhances the activity of the $Na^+/Ca^{2+}$ exchanger on the basolateral membrane, which pumps $Na^+$ into the cell and $Ca^{2+}$ out into the blood. * **Result:** This leads to increased reabsorption of calcium from the tubular fluid, thereby **decreasing urinary calcium excretion** (hypocalciuria). By lowering the concentration of calcium in the urine, Thiazides prevent the formation of calcium oxalate stones. **Analysis of Incorrect Options:** * **A. Allopurinol:** A xanthine oxidase inhibitor used for hyperuricemia and uric acid stones, but it does not directly affect renal calcium handling. * **B. Furosemide:** A loop diuretic that inhibits the $Na^+/K^+/2Cl^-$ cotransporter. It **increases** urinary calcium excretion ("Loops Lose Calcium") and is actually used to treat hypercalcemia. It would worsen hypercalciuria. * **C. Acetazolamide:** A carbonic anhydrase inhibitor. It increases urinary bicarbonate and can lead to alkaline urine, which actually promotes the precipitation of calcium phosphate stones. **NEET-PG High-Yield Pearls:** * **Mnemonic:** "Loops Lose calcium, Thiazides Thank (retain) calcium." * **Clinical Use:** Thiazides are unique because they are the only diuretics that cause **hypocalciuria**. * **Side Effects:** Remember the "4 Hypers" of Thiazides: Hyperglycemia, Hyperlipidemia, Hyperuricemia, and **Hypercalcemia**. * **Drug of Choice:** For Nephrogenic Diabetes Insipidus, Thiazides are also the preferred treatment.

Question 32: Paradoxical action is seen with which of the following diuretics?

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

Explanation: **Explanation:** The "paradoxical action" of **Thiazide diuretics** refers to their ability to **reduce urine volume** in patients with **Diabetes Insipidus (DI)**, despite being diuretics that normally increase urine output in healthy individuals. **Mechanism of Paradoxical Action:** In Diabetes Insipidus, there is a deficiency or resistance to ADH, leading to the excretion of large volumes of dilute urine. Thiazides inhibit the Na⁺-Cl⁻ symporter in the distal convoluted tubule, causing mild natriuresis. This leads to a slight depletion of total body sodium and a decrease in extracellular fluid (ECF) volume. In response, the proximal tubule increases the reabsorption of water and sodium to compensate. Consequently, less fluid reaches the distal parts of the nephron, resulting in a net reduction in final urine volume. **Analysis of Incorrect Options:** * **B & C (Triamterene & Spironolactone):** These are potassium-sparing diuretics. While they act on the late distal tubule and collecting duct, they do not exhibit this specific paradoxical effect in DI. * **D (Furosemide):** This is a potent loop diuretic. It is contraindicated in DI because it interferes with the medullary osmotic gradient, further impairing the kidney's ability to concentrate urine and potentially worsening dehydration. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Thiazides (specifically Chlorthalidone or Hydrochlorothiazide) are the treatment of choice for **Nephrogenic Diabetes Insipidus**. * **Electrolyte Side Effects:** Remember the "4 Hypo, 2 Hyper" rule for Thiazides: **Hypo**kalemia, **Hypo**natremia, **Hypo**magnesemia, **Hypo**chloremic alkalosis; **Hyper**uricemia, and **Hyper**calcemia (unlike Loop diuretics which cause hypocalcemia). * **Lithium-Induced DI:** Amiloride is the preferred agent for DI specifically caused by Lithium toxicity.

Question 33: Which drug leads to glucose intolerance?

A. Hydrochlorothiazide (Correct Answer)
B. ACE inhibitors
C. Verapamil
D. Sulfonylureas

Explanation: **Explanation:** **Hydrochlorothiazide (HCTZ)**, a thiazide diuretic, is well-known for causing metabolic side effects, including **hyperglycemia (glucose intolerance)**. The underlying mechanism is twofold: 1. **Hypokalemia-induced inhibition of insulin:** Thiazides cause potassium depletion. Low extracellular potassium levels inhibit the release of insulin from the pancreatic $\beta$-cells. 2. **Decreased peripheral glucose uptake:** Thiazides can reduce peripheral sensitivity to insulin. Consequently, they should be used with caution in patients with diabetes mellitus or pre-diabetes. **Analysis of Incorrect Options:** * **B. ACE Inhibitors:** These drugs (e.g., Enalapril) actually **improve** insulin sensitivity and are renoprotective. They are the preferred antihypertensives in diabetic patients. * **C. Verapamil:** This is a Calcium Channel Blocker (CCB). While some CCBs can theoretically interfere with insulin release at very high doses, they are generally considered metabolically neutral in clinical practice. * **D. Sulfonylureas:** These are oral hypoglycemic agents (e.g., Glibenclamide) used to **treat** diabetes by stimulating insulin secretion. They decrease blood glucose rather than causing intolerance. **NEET-PG High-Yield Pearls:** * **Thiazide Metabolic Profile:** Remember the mnemonic **"Hyper-GLUC"**—Thiazides cause **Hyper**glycemia, **Hyper**lipidemia, **Hyper**uricemia (can precipitate Gout), and **Hyper**calcemia. * **Electrolyte Profile:** Unlike Loop diuretics (which cause hypocalcemia), Thiazides cause **hypocalciuria** (useful in treating recurrent calcium stones). * **Drug of Choice:** ACE inhibitors or ARBs are the first-line antihypertensives for diabetics to prevent diabetic nephropathy.

Question 34: Spironolactone is the first drug to be given for which condition?

A. Cirrhotic edema (Correct Answer)
B. Cardiac edema
C. Idiopathic edema
D. Nutritional edema

Explanation: ### Explanation **Correct Option: A. Cirrhotic edema** Spironolactone is the **drug of choice (DOC)** for edema associated with liver cirrhosis. In cirrhosis, there is decreased hepatic clearance of aldosterone and activation of the Renin-Angiotensin-Aldosterone System (RAAS) due to peripheral vasodilation. This leads to **secondary hyperaldosteronism**, causing significant sodium and water retention. As a competitive aldosterone antagonist, Spironolactone directly counteracts this mechanism. It is preferred over loop diuretics because it prevents the hypokalemia that can trigger hepatic encephalopathy. **Analysis of Incorrect Options:** * **B. Cardiac edema:** While Spironolactone (and Eplerenone) reduces mortality in chronic heart failure (NYHA Class II-IV), the first-line drug for symptomatic relief of acute cardiac edema/congestive heart failure is a **Loop diuretic** (e.g., Furosemide) due to its rapid and potent action. * **C. Idiopathic edema:** This condition, typically seen in fluid-retaining women, is primarily managed with weight reduction and salt restriction. If drugs are used, Spironolactone is an option, but it is not the classic "first drug" association compared to cirrhosis. * **D. Nutritional edema:** This is primarily managed by correcting the underlying protein deficiency (hypoalbuminemia) and nutritional status rather than primary diuretic therapy. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Competitive antagonist of Mineralocorticoid Receptors in the late distal tubule and collecting duct. * **Side Effects:** The most common is **Hyperkalemia**. Due to its non-specific binding to androgen receptors, it causes **Gynecomastia** and impotence in males (Eplerenone is a more specific alternative without these effects). * **Other DOC uses:** Spironolactone is also the DOC for **Conn’s Syndrome** (Primary Hyperaldosteronism). * **Dosing Tip:** In cirrhosis, it is often used in a 100:40 ratio with Furosemide to maintain potassium balance.

Question 35: Which of the following is a non-competitive inhibitor of carbonic anhydrase?

A. Allopurinol
B. Acetazolamide (Correct Answer)
C. Bimatoprost
D. Dipivefrine

Explanation: ### Explanation **Correct Option: B. Acetazolamide** Acetazolamide is a sulfonamide derivative that acts as a potent, **non-competitive inhibitor** of the enzyme **carbonic anhydrase (CA)**, primarily the Type II isoenzyme found in the proximal convoluted tubule (PCT) and the ciliary body of the eye. By inhibiting CA, it prevents the dehydration of $H_2CO_3$ and the rehydration of $CO_2$, leading to a decrease in $H^+$ secretion and a subsequent increase in the excretion of sodium, potassium, and bicarbonate. This results in alkaline urine and a mild metabolic acidosis. **Analysis of Incorrect Options:** * **A. Allopurinol:** This is a hypuricemic agent that acts as a competitive inhibitor of **Xanthine Oxidase**. It is used in the chronic management of Gout. * **C. Bimatoprost:** This is a **Prostaglandin $F_{2\alpha}$ analogue**. It reduces intraocular pressure by increasing the uveoscleral outflow of aqueous humor, rather than inhibiting CA. * **D. Dipivefrine:** This is a prodrug of **Epinephrine**. It acts as a sympathomimetic to reduce intraocular pressure by increasing aqueous outflow; it does not inhibit enzymes. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Acetazolamide is the DOC for **Acute Mountain Sickness** (prevents cerebral/pulmonary edema and counteracts respiratory alkalosis). * **Glaucoma:** Used to rapidly decrease intraocular pressure in acute angle-closure glaucoma by reducing aqueous humor formation. * **Side Effects:** Drowsiness, paresthesia, and the formation of **calcium phosphate renal stones** (due to alkaline urine). * **Contraindication:** Avoid in patients with hepatic cirrhosis, as it can precipitate **hepatic encephalopathy** by decreasing ammonia excretion.

Question 36: A 65-year-old male with CHF exacerbation is given IV furosemide. Which of the following adverse events are not associated with this medication?

A. Hypotension
B. Hyperkalemia (Correct Answer)
C. Worsening renal function
D. Transient neurotoxicity from high dose

Explanation: **Explanation:** **Furosemide** is a potent **Loop Diuretic** that acts by inhibiting the **Na⁺-K⁺-2Cl⁻ symporter** in the Thick Ascending Limb (TAL) of the Loop of Henle. **Why Hyperkalemia is the Correct Answer:** Loop diuretics increase the delivery of sodium (Na⁺) to the distal convoluted tubule and collecting duct. This stimulates the exchange of Na⁺ for Potassium (K⁺) and Hydrogen (H⁺) ions under the influence of aldosterone. Consequently, there is increased urinary excretion of potassium, leading to **Hypokalemia**, not hyperkalemia. It also causes metabolic alkalosis. **Analysis of Incorrect Options:** * **A. Hypotension:** Potent diuresis leads to significant intravascular volume depletion, which can cause orthostatic hypotension or acute circulatory collapse. * **C. Worsening renal function:** Excessive diuresis can lead to "pre-renal azotemia" due to reduced renal perfusion pressure. * **D. Transient neurotoxicity:** High-dose IV furosemide can cause **ototoxicity** (damage to the 8th cranial nerve), manifesting as tinnitus or hearing loss. This is due to electrolyte imbalances in the endolymph and is often transient but can be permanent if combined with aminoglycosides. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Loop Diuretic Side Effects (OH DANG!):** **O**totoxicity, **H**ypokalemia, **D**ehydration, **A**llergy (Sulfa), **N**ephritis (Interstitial), **G**out (Hyperuricemia). * **Calcium Effect:** Unlike Thiazides (which cause hypercalcemia), Loop diuretics cause **Hypocalcemia** ("Loops Lose Calcium"). * **Drug of Choice:** IV Furosemide is the first-line treatment for **Acute Pulmonary Edema** due to its rapid venodilatory effect (mediated by prostaglandins) followed by diuresis.

Question 37: Which of the following diuretics causes maximum loss of potassium in urine?

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

Explanation: **Explanation:** The correct answer is **Acetazolamide**. While many diuretics cause hypokalemia, Acetazolamide (a Carbonic Anhydrase Inhibitor) typically causes the **maximum** loss of potassium in the urine per unit of sodium excreted. **Why Acetazolamide is correct:** Acetazolamide acts on the proximal convoluted tubule (PCT), inhibiting the reabsorption of sodium bicarbonate ($NaHCO_3$). This leads to a massive delivery of sodium and non-reabsorbable bicarbonate ions to the distal nephron. To compensate for the high sodium load, the distal tubule increases sodium-potassium exchange via aldosterone-sensitive channels. Furthermore, the presence of bicarbonate (an anion) in the distal tubule increases the lumen-negative potential, which further "pulls" potassium out of the cells into the urine. **Why the other options are incorrect:** * **Spironolactone:** This is a potassium-sparing diuretic. It antagonizes aldosterone, leading to potassium **retention** (hyperkalemia), not loss. * **Furosemide & Ethacrynic Acid:** These are Loop Diuretics. While they cause significant hypokalemia by inhibiting the $Na^+-K^+-2Cl^-$ symporter and increasing distal sodium delivery, the magnitude of potassium loss relative to bicarbonate-driven excretion in CA inhibitors is generally lower. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Action:** Acetazolamide acts on the PCT; Loop diuretics on the Thick Ascending Limb (TAL); Thiazides on the Distal Convoluted Tubule (DCT). * **Metabolic Effect:** Acetazolamide causes **Hyperchloremic Metabolic Acidosis**, whereas Loop and Thiazide diuretics cause **Metabolic Alkalosis**. * **Therapeutic Uses:** Acetazolamide is the drug of choice for Glaucoma (decreases aqueous humor) and Mountain Sickness (induces metabolic acidosis to stimulate respiration).

Question 38: Which of the following is a mineralocorticoid antagonist?

A. Spironolactone (Correct Answer)
B. Inamrinone
C. Nicorandil
D. Ketorolac

Explanation: **Explanation:** **Spironolactone (Option A)** is the correct answer. It is a synthetic steroid that acts as a competitive antagonist of the **Mineralocorticoid Receptor (MR)** in the late distal tubule and collecting duct of the kidney. By blocking the action of aldosterone, it inhibits the synthesis of Na+/K+ ATPase and epithelial sodium channels (ENaC). This results in the excretion of sodium and water while retaining potassium, categorizing it as a **Potassium-Sparing Diuretic**. **Analysis of Incorrect Options:** * **Inamrinone (Option B):** A Phosphodiesterase-3 (PDE3) inhibitor. It acts as an inodilator (positive inotrope and vasodilator) used in the management of acute heart failure. * **Nicorandil (Option C):** A dual-action drug that acts as a Potassium channel opener and a nitric oxide donor. It is primarily used as an anti-anginal agent. * **Ketorolac (Option D):** A potent Non-Steroidal Anti-Inflammatory Drug (NSAID) that inhibits cyclooxygenase (COX) enzymes, used for short-term management of moderate to severe pain. **High-Yield Clinical Pearls for NEET-PG:** * **Eplerenone** is a more selective mineralocorticoid antagonist with fewer endocrine side effects (like gynecomastia) compared to spironolactone. * **Clinical Uses:** Spironolactone is the drug of choice for **Primary Hyperaldosteronism (Conn’s Syndrome)** and edema associated with **Liver Cirrhosis**. It also improves survival in Chronic Heart Failure (NYHA Class II-IV). * **Side Effects:** The most significant side effect is **Hyperkalemia**. Due to its non-selective binding to androgen and progesterone receptors, it can cause gynecomastia, impotence, and menstrual irregularities.

Question 39: Which of the following adverse effects is NOT caused by furosemide?

A. Hyperglycemia
B. Hypomagnesemia
C. Hypokalemia
D. Acidosis (Correct Answer)

Explanation: Furosemide is a high-ceiling loop diuretic that acts by inhibiting the **Na⁺-K⁺-2Cl⁻ symporter** in the Thick Ascending Limb (TAL) of the Loop of Henle [1]. **Why Acidosis is the Correct Answer:** Furosemide does **not** cause acidosis; instead, it causes **Metabolic Alkalosis** [1, 3]. This occurs via two mechanisms: 1. **Contraction Alkalosis:** Loss of isotonic fluid (NaCl and water) leads to a decrease in extracellular fluid volume, concentrating the remaining bicarbonate [3]. 2. **Increased H⁺ secretion:** Increased delivery of Na⁺ to the distal tubule stimulates Na⁺ reabsorption in exchange for H⁺ and K⁺ (via aldosterone), leading to net acid loss in the urine [1, 3]. **Analysis of Incorrect Options:** * **Hyperglycemia:** Loop diuretics can impair insulin release from the pancreas and decrease peripheral glucose utilization, often secondary to hypokalemia. * **Hypomagnesemia:** By abolishing the positive transepithelial potential in the TAL, loop diuretics inhibit the paracellular reabsorption of divalent cations (Mg²⁺ and Ca²⁺) [1, 2]. * **Hypokalemia:** Increased Na⁺ delivery to the distal nephron promotes K⁺ excretion via the Na⁺/K⁺ exchange pump, a classic side effect of all diuretics acting proximal to the collecting duct [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Loop Diuretic Side Effects (OH DANG!):** **O**totoxicity, **H**ypokalemia, **D**ehydration, **A**llergy (Sulfa), **N**ephritis (Interstitial), **G**out (Hyperuricemia) [2]. * **Calcium Handling:** Loop diuretics cause **Hypocalcemia** ("Loops Lose Calcium") [1], whereas Thiazides cause **Hypercalcemia**. * **Drug of Choice:** Furosemide is the drug of choice for acute pulmonary edema and symptomatic hypercalcemia.

Question 40: Which intravenous fluid contains the maximum amount of potassium and is preferred for treating hypokalemia?

A. Ringer lactate
B. Isolyte-P
C. Isotonic saline
D. Isolyte-M (Correct Answer)

Explanation: **Explanation:** The correct answer is **Isolyte-M**. The management of electrolyte imbalances requires a precise understanding of the ionic composition of various intravenous fluids. **Why Isolyte-M is correct:** Isolyte-M (Maintenance solution) is specifically designed to provide maintenance electrolytes. It contains the highest concentration of potassium among the common IV fluids listed, typically providing **40 mEq/L** of Potassium ($K^+$). This makes it the preferred choice for treating or preventing hypokalemia when oral supplementation is not feasible. **Analysis of Incorrect Options:** * **Ringer Lactate (RL):** Often called a "balanced" salt solution, it contains only **4 mEq/L** of Potassium. While it is physiological, the concentration is too low to effectively correct significant hypokalemia. * **Isolyte-P (Pediatric):** Designed for pediatric maintenance, it contains approximately **20 mEq/L** of Potassium. While higher than RL, it is still lower than the concentration found in Isolyte-M. * **Isotonic Saline (0.9% NaCl):** This solution contains **zero** potassium. It consists only of Sodium (154 mEq/L) and Chloride (154 mEq/L). **High-Yield Clinical Pearls for NEET-PG:** * **Maximum Infusion Rate:** In a peripheral vein, the maximum concentration of $K^+$ should generally not exceed **40 mEq/L**, and the rate of infusion should not exceed **10–20 mEq/hour** to avoid cardiac arrhythmias and phlebitis. * **Isolyte-G:** Contains high Gastric replacement electrolytes (contains $NH_4Cl$); do not confuse with Isolyte-M. * **ECG in Hypokalemia:** Look for flattened T-waves, prominent **U-waves**, and ST-segment depression. * **Refractory Hypokalemia:** If hypokalemia does not respond to replacement, always check **Magnesium** levels; hypomagnesemia often coexists and hinders $K^+$ correction.

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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

Practice Questions

Osmotic Diuretics

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Combination Diuretic Therapy

Practice Questions

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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