Diuretics Practice Questions

Q: Dorzolamide is a:

Topically applied ocular carbonic anhydrase inhibitor. **Explanation:** **Dorzolamide** is a potent, highly specific inhibitor of the enzyme **Carbonic Anhydrase (Type II)**. In the eye, carbonic anhydrase is essential for the production of aqueous humor by the ciliary body epithelium. By inhibiting this enzyme, Dorzolamide reduces the secretion of aqueous humor, thereby lowering intraocular pressure (IOP). It is specifically designed for **topical application** as an ophthalmic solution to avoid the systemic side effects (like metabolic acidosis or electrolyte imbalance) associated with oral carbonic anhydrase inhibitors like Acetazolamide. **Analysis of Incorrect Options:** * **Option A:** Second-generation sulfonylureas (e.g., Glibenclamide, Glipizide) are used for Type 2 Diabetes. While Dorzolamide shares a sulfonamide structure, it has no hypoglycemic activity. * **Option B:** Although Dorzolamide is a sulfonamide derivative, it lacks clinically significant antimicrobial activity. Topical sulfonamide antibacterials include drugs like Sulfacetamide. * **Option C:** Luminal amoebicides (e.g., Diloxanide furoate, Iodoquinol) act within the bowel lumen to treat intestinal amoebiasis; they are unrelated to carbonic anhydrase inhibition. **High-Yield Clinical Pearls for NEET-PG:** * **Indications:** Primarily used in Open-Angle Glaucoma and Ocular Hypertension. * **Side Effects:** The most common side effect is a **bitter taste (dysgeusia)** following application due to drainage through the nasolacrimal duct. It can also cause local stinging and superficial punctate keratitis. * **Contraindication:** Avoid in patients with known **sulfonamide hypersensitivity**. * **Brinzolamide** is another topical carbonic anhydrase inhibitor; it is often preferred over Dorzolamide as it causes less ocular stinging.

Q: Which of the following statements about diuretics is NOT true?

Acetazolamide is a carbonic anhydrase stimulant.. ### Explanation **1. Why Option A is the Correct Answer (The "Not True" Statement):** Acetazolamide is a **Carbonic Anhydrase (CA) Inhibitor**, not a stimulant. It works in the proximal convoluted tubule (PCT) by inhibiting the enzyme carbonic anhydrase. This prevents the dehydration of carbonic acid and the reabsorption of bicarbonate ($HCO_3^-$), leading to alkaline diuresis. Because it inhibits the enzyme, the statement claiming it is a "stimulant" is factually incorrect. **2. Analysis of Other Options:** * **Option B (Thiazides):** This is **true**. Thiazides act on the early distal convoluted tubule (DCT), which is also known as the **cortical diluting segment**. They inhibit the $Na^+-Cl^-$ symporter. * **Option C (Furosemide):** This is **true**. Furosemide is a loop diuretic that acts on the thick ascending limb of Henle. It is called "high-ceiling" because it has a steep dose-response curve, meaning increasing the dose leads to a proportional increase in diuresis over a wide range. * **Option D (Spironolactone):** This is **true**. It is a potassium-sparing diuretic that competitively inhibits the **aldosterone receptor** (Mineralocorticoid receptor) in the late DCT and collecting ducts. **3. NEET-PG High-Yield Clinical Pearls:** * **Acetazolamide Uses:** Glaucoma (decreases aqueous humor), Mountain sickness (induces metabolic acidosis to stimulate respiration), and Urinary alkalization. * **Side Effects:** Metabolic acidosis, hypokalemia, and sulfonamide-like hypersensitivity. * **Thiazide Paradox:** While they are diuretics, they are used to treat **Diabetes Insipidus** because they reduce glomerular filtration and increase proximal salt/water reabsorption. * **Furosemide Side Effects:** Remember the mnemonic **OH DANG**: **O**totoxicity, **H**ypokalemia, **D**ehydration, **A**llergy (sulfa), **N**ephritis, **G**out (hyperuricemia).

Q: All of the following diuretics inhibit the Na+-K+-2Cl- symporter, except?

Thiazide. The question tests the knowledge of the site of action and molecular targets of various diuretics. 1. Why Thiazide is the Correct Answer: Thiazide diuretics (e.g., Hydrochlorothiazide, Chlorthalidone) act on the **Distal Convoluted Tubule (DCT)** [1]. Their primary mechanism is the inhibition of the **Na+-Cl- symporter** (NCC) on the luminal membrane [1, 3]. They do not affect the Na+-K+-2Cl- (NKCC2) transporter [3]. 2. Analysis of Incorrect Options (Loop Diuretics): The other three options belong to the class of **Loop Diuretics**, which specifically inhibit the **Na+-K+-2Cl- (NKCC2) symporter** in the Thick Ascending Limb (TAL) of the Loop of Henle [2, 4]: * **Furosemide:** A prototype high-ceiling loop diuretic (Sulfonamide derivative). * **Ethacrynic acid:** A phenoxyacetic acid derivative. It is a non-sulfonamide loop diuretic, making it the drug of choice for patients with sulfonamide allergies. * **Mersalyl:** An older organomercurial diuretic that also acts on the TAL to inhibit the same symporter, though it is now obsolete due to toxicity. Clinical Pearls for NEET-PG: * **Site of Action:** Loop diuretics act on the TAL (medullary and cortical), while Thiazides act on the cortical DCT. * **Calcium Handling:** This is a high-yield differentiator. Loop diuretics cause **Hypercalciuria** (used in treating hypercalcemia), whereas Thiazides cause **Hypocalciuria** (used in treating calcium nephrolithiasis). * **Ototoxicity:** Ethacrynic acid is the most ototoxic loop diuretic. * **Metabolic Side Effects:** Both classes can cause hypokalemia and metabolic alkalosis.

Q: Which of the following antihypertensive agents is contraindicated in patients with chronic renal disease?

Hydrochlorothiazide-triamterene. **Explanation:** The correct answer is **A. Hydrochlorothiazide-triamterene**. **Why it is correct:** This combination contains **Triamterene**, a potassium-sparing diuretic. In chronic renal disease (CRD), the kidneys' ability to excrete potassium is significantly impaired. Using potassium-sparing agents like triamterene, amiloride, or spironolactone in these patients poses a high risk of life-threatening **hyperkalemia**. Furthermore, **Thiazides** (like Hydrochlorothiazide) lose their efficacy as monotherapy when the Glomerular Filtration Rate (GFR) falls below 30 mL/min, making this combination both dangerous and ineffective in advanced renal failure. **Why the other options are incorrect:** * **B. Furosemide:** This is a loop diuretic and is the **diuretic of choice** in patients with renal impairment. Unlike thiazides, loop diuretics remain effective even at low GFR levels and help manage fluid overload in CRD. * **C. Prazosin:** This is an alpha-1 blocker. It is primarily metabolized by the liver and does not require significant dose adjustment in renal failure, making it safe for use. * **D. Nifedipine:** This is a Calcium Channel Blocker (CCB). CCBs are generally safe in renal disease as they do not adversely affect renal hemodynamics and are often used to manage hypertension in these patients. **High-Yield Clinical Pearls for NEET-PG:** * **Hyperkalemia Risk:** Always avoid the "K-SPARE" drugs (Spironolactone, Amiloride, Triamterene) and ACE inhibitors/ARBs in patients with advanced renal failure or high baseline potassium. * **Thiazide Limit:** Thiazides are generally ineffective if **CrCl < 30 mL/min** (Exception: Metolazone). * **Drug of Choice:** Loop diuretics (Furosemide) are preferred for edema/hypertension in renal insufficiency.

Q: Furosemide is useful in:

Refractory oedema.. **Explanation:** **1. Why "Refractory Oedema" is correct:** 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. It is known as a "high-ceiling" diuretic because it has a steep dose-response curve; increasing the dose leads to a progressive increase in diuresis. This makes it the drug of choice for **refractory oedema** (oedema not responding to milder diuretics) associated with Congestive Heart Failure, Nephrotic Syndrome, and Chronic Renal Failure. **2. Why other options are incorrect:** * **A. Hypertension:** While loop diuretics can be used in hypertension complicated by renal failure, **Thiazides** are the first-line diuretic for essential hypertension due to their longer duration of action and vasodilator properties. * **C. Hypocalcemia:** Furosemide increases the urinary excretion of calcium ("Loop loses Calcium"). Therefore, it is used to treat **Hypercalcemia**, not hypocalcemia. * **D. Hypokalemia:** Furosemide causes significant potassium loss in the urine. It is a *cause* of hypokalemia, not a treatment for it. **3. High-Yield NEET-PG Pearls:** * **Mechanism:** Inhibits Na⁺-K⁺-2Cl⁻ (NKCC2) in the TAL. * **Electrolyte Profile:** Causes Hypokalemia, Hypomagnesemia, and **Hypocalcemia**. * **Ototoxicity:** This is a unique side effect of loop diuretics, especially when used with aminoglycosides. * **Acute Pulmonary Oedema:** Furosemide is the drug of choice here, not just for its diuretic effect, but for its rapid **venodilatory action** (mediated by prostaglandins), which reduces cardiac preload.

Q: Hyperkalemia is caused by all EXCEPT:

Loop diuretics. ### Explanation The correct answer is **Loop diuretics** because they cause **hypokalemia** (low potassium), not hyperkalemia. #### 1. Why Loop Diuretics (Option A) are the Correct Answer: Loop diuretics (e.g., Furosemide) inhibit the **Na⁺-K⁺-2Cl⁻ symporter** in the Thick Ascending Limb of the Loop of Henle. This leads to a massive delivery of sodium to the distal tubule. To reabsorb this sodium, the distal tubule activates the Na⁺/K⁺ exchange mechanism (driven by aldosterone), which results in the **excretion of potassium** into the urine. This process, combined with volume depletion-induced secondary hyperaldosteronism, leads to hypokalemia. #### 2. Why the other options are incorrect (They cause Hyperkalemia): * **Amiloride (Option C):** This is a potassium-sparing diuretic that blocks the **ENaC (Epithelial Sodium Channels)** in the collecting duct. By preventing sodium reabsorption, it reduces the negative luminal potential, thereby inhibiting the secretion of potassium into the lumen. * **Enalapril (Option D) & Valsartan (Option B):** Enalapril (an ACE inhibitor) and Valsartan (an ARB) both interfere with the **Renin-Angiotensin-Aldosterone System (RAAS)**. By decreasing aldosterone levels or blocking its action, they prevent potassium excretion in the distal nephron, leading to potassium retention. #### 3. NEET-PG High-Yield Pearls: * **Diuretics causing Hypokalemia:** Loop diuretics and Thiazides. * **Diuretics causing Hyperkalemia:** Spironolactone, Eplerenone (Aldosterone antagonists), Amiloride, and Triamterene. * **Clinical Tip:** Always monitor serum potassium when combining ACE inhibitors with potassium-sparing diuretics, as this significantly increases the risk of life-threatening hyperkalemia. * **ECG in Hyperkalemia:** Look for "Tall tented T-waves" and "Widened QRS complex."

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

Thiazide. ### 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.

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

Thiazide. **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.

Q: Acetazolamide decreases intraocular pressure by what mechanism?

Decreases aqueous humor production. **Explanation:** **Mechanism of Action (Why A is correct):** Acetazolamide is a potent **Carbonic Anhydrase Inhibitor (CAI)**. In the eye, the enzyme carbonic anhydrase is present in the non-pigmented ciliary epithelium. It facilitates the reaction: $CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^-$. The secretion of aqueous humor is an active process dependent on the transport of sodium and bicarbonate ions. By inhibiting carbonic anhydrase, acetazolamide reduces the availability of bicarbonate ions, which in turn decreases the active transport of sodium into the posterior chamber. This osmotic shift leads to a **reduction in aqueous humor production by approximately 50-60%**, thereby lowering intraocular pressure (IOP). **Analysis of Incorrect Options:** * **B. Decreases vitreous volume:** This is the mechanism of **Hyperosmotic agents** (e.g., Mannitol, Glycerol). They create an osmotic gradient that draws water out of the vitreous into the bloodstream. * **C. Increased drainage of aqueous:** This is the mechanism of **Miotics** (pilocarpine - increases trabecular outflow) or **Prostaglandin analogues** (latanoprost - increases uveoscleral outflow). Acetazolamide has no effect on the outflow pathways. **High-Yield Clinical Pearls for NEET-PG:** * **Route:** Systemic (Oral/IV). Topical CAIs include Dorzolamide and Brinzolamide. * **Indications:** Acute Angle Closure Glaucoma (emergency management) and prophylaxis before intraocular surgery. * **Side Effects:** Paresthesia (most common), metabolic acidosis, hypokalemia, and renal calculi. * **Contraindication:** It is a sulfonamide derivative; avoid in patients with **sulfa allergy** and those with severe hepatic or renal impairment.

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

Acetazolamide. ### 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 1

Dorzolamide is a:

Accepted Answer

Topically applied ocular carbonic anhydrase inhibitor

Answer

Second generation sulfonylurea hypoglycaemic

Answer

Topical sulfonamide antibacterial

Answer

Luminal amoebicide

Question 2

Which of the following statements about diuretics is NOT true?

Accepted Answer

Acetazolamide is a carbonic anhydrase stimulant.

Answer

Thiazides act on the cortical diluting segment of the nephron.

Answer

Furosemide is a high-ceiling diuretic.

Answer

Spironolactone is an aldosterone antagonist.

Question 3

All of the following diuretics inhibit the Na+-K+-2Cl- symporter, except?

Accepted Answer

Thiazide

Answer

Furosemide

Answer

Ethacrynic acid

Answer

Mersalyl

Question 4

Which of the following antihypertensive agents is contraindicated in patients with chronic renal disease?

Accepted Answer

Hydrochlorothiazide-triamterene

Answer

Furosemide

Answer

Prazosin

Answer

Nifedipine

Question 5

Furosemide is useful in:

Accepted Answer

Refractory oedema.

Answer

Hypertension.

Answer

Hypocalcemia.

Answer

Hypokalemia.

Question 6

Hyperkalemia is caused by all EXCEPT:

Accepted Answer

Loop diuretics

Answer

Valsartan

Answer

Amiloride

Answer

Enalapril

Question 7

Which drug is used in the treatment of idiopathic hypercalciuria?

Accepted Answer

Thiazide

Answer

Allopurinol

Answer

Furosemide

Answer

Acetazolamide

Question 8

Paradoxical action is seen with which of the following diuretics?

Accepted Answer

Thiazide

Answer

Triamterene

Answer

Spironolactone

Answer

Furosemide

Question 9

Acetazolamide decreases intraocular pressure by what mechanism?

Accepted Answer

Decreases aqueous humor production

Answer

Decreases vitreous volume

Answer

Increased drainage of aqueous

Answer

None of the above

Question 10

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

Accepted Answer

Acetazolamide

Answer

Allopurinol

Answer

Bimatoprost

Answer

Dipivefrine

Diuretics — MCQs

Diuretics — MCQs

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