Diuretics Practice Questions

Q: Mannitol when given intravenously causes which of the following changes?

Decrease in blood viscosity. **Explanation:** Mannitol is an osmotic diuretic that remains confined to the extracellular compartment. When administered intravenously, it creates an osmotic gradient that draws water from the intracellular space into the vascular compartment. **1. Why Option A is Correct:** The rapid shift of water from cells into the bloodstream leads to **hemodilution**. This expansion of plasma volume decreases the hematocrit and reduces the overall **blood viscosity**. This reduction in viscosity is clinically significant as it improves microcirculatory blood flow, particularly in the brain, which is one of the mechanisms by which mannitol reduces intracranial pressure (ICP). **2. Why the other options are incorrect:** * **Option B:** Mannitol decreases viscosity via hemodilution; it does not increase it. * **Option C:** While mannitol can increase renal blood flow, it does not consistently increase the **Glomerular Filtration Rate (GFR)**. In fact, its primary site of action is the Loop of Henle and the proximal tubule, where it limits water reabsorption. * **Option D:** Mannitol is used to **decrease** Intracranial Tension (ICT) and Intraocular Pressure (IOP) by drawing fluid out of the brain parenchyma and vitreous humor into the blood. It does not increase ICT. **High-Yield NEET-PG Pearls:** * **Mechanism:** Osmotic effect in the proximal tubule and descending limb of the Loop of Henle. * **Contraindications:** Acute Pulmonary Edema and Congestive Heart Failure (due to the initial rapid expansion of extracellular fluid volume) and Anuria. * **Clinical Uses:** Cerebral edema (to lower ICT), acute congestive glaucoma (to lower IOP), and prevention of cisplatin-induced nephrotoxicity. * **Side Effect:** Acute expansion of ECF can lead to "dialysis disequilibrium" or pulmonary congestion.

Q: Acetazolamide is administered to a glaucoma patient. Given that this drug inhibits carbonic anhydrase in the renal proximal tubule, which of the following substances will be excreted at a lower rate?

NH4+. **Explanation:** **Mechanism of Action & The Correct Answer (NH4+):** Acetazolamide is a Carbonic Anhydrase (CA) inhibitor. In the proximal convoluted tubule (PCT), CA is essential for the reabsorption of bicarbonate ($HCO_3^-$) and the secretion of Hydrogen ions ($H^+$). By inhibiting CA, the drug reduces the availability of $H^+$ ions in the tubular lumen. Ammonia ($NH_3$) is produced by tubular cells and diffuses into the lumen, where it normally combines with secreted $H^+$ to form Ammonium ($NH_4^+$). This process, known as **"Ammonia Trapping,"** renders the molecule non-diffusible, ensuring its excretion. Since Acetazolamide decreases $H^+$ secretion, $NH_3$ cannot be converted to $NH_4^+$. Consequently, $NH_4^+$ formation decreases, and $NH_3$ diffuses back into the systemic circulation. Therefore, the **excretion rate of $NH_4^+$ decreases.** **Why Other Options are Incorrect:** * **A & B (Na+ and H2O):** Inhibition of CA prevents $NaHCO_3$ reabsorption. This leads to increased luminal osmolarity, causing **Natriuresis** (increased $Na^+$ excretion) and **Diuresis** (increased $H_2O$ excretion). * **C (HCO3-):** The primary effect of Acetazolamide is the inhibition of $HCO_3^-$ reabsorption, leading to significant **Bicarbonaturia** (increased $HCO_3^-$ excretion) and subsequent hyperchloremic metabolic acidosis. **High-Yield NEET-PG Pearls:** * **Clinical Uses:** Glaucoma (decreases aqueous humor), Mountain Sickness (induces metabolic acidosis to stimulate respiration), and Urinary Alkalinization (to excrete acidic drugs like uric acid). * **Side Effects:** Hypokalemia, Metabolic Acidosis, and **Hyperammonemia** (contraindicated in Liver Cirrhosis as it can precipitate hepatic encephalopathy due to decreased $NH_4^+$ excretion). * **Site of Action:** Proximal Convoluted Tubule (PCT).

Q: Acetazolamide acts at which part of the nephron?

Proximal Convoluted Tubule (PCT). **Explanation:** **Acetazolamide** is a potent **Carbonic Anhydrase (CA) inhibitor** [2]. Its primary site of action is the **Proximal Convoluted Tubule (PCT)** [4]. In the PCT, carbonic anhydrase (specifically the CA-IV isoenzyme on the brush border and CA-II in the cytoplasm) is responsible for the reabsorption of sodium bicarbonate ($NaHCO_3$) [3]. By inhibiting this enzyme, acetazolamide prevents the dehydration of carbonic acid and the subsequent reabsorption of bicarbonate, leading to alkaline diuresis and a mild diuretic effect [2]. **Analysis of Incorrect Options:** * **Distal Convoluted Tubule (DCT):** This is the site of action for **Thiazide diuretics**, which inhibit the $Na^+/Cl^-$ symporter. * **Ascending loop of Henle:** Specifically the Thick Ascending Limb (TAL), this is the site of action for **Loop diuretics** (e.g., Furosemide), which inhibit the $Na^+/K^+/2Cl^-$ cotransporter. * **Descending loop of Henle:** This segment is highly permeable to water but impermeable to solutes; it is primarily influenced by **Osmotic diuretics** like Mannitol [1]. **Clinical Pearls for NEET-PG:** * **Therapeutic Uses:** Glaucoma (decreases aqueous humor production), Acute Mountain Sickness (counteracts respiratory alkalosis), and Urinary Alkalinization (to excrete acidic drugs like uric acid or cystine). * **Adverse Effects:** Hyperchloremic metabolic acidosis, hypokalemia, and paresthesia. * **Contraindications:** Avoid in patients with hepatic cirrhosis, as it can decrease ammonia excretion, potentially precipitating hepatic encephalopathy.

Q: What is the mechanism of action of furosemide as a diuretic?

Inhibition of Na-K-Cl ion symporter. **Explanation:** **1. Why Option A is Correct:** Furosemide is a potent **Loop Diuretic**. Its primary mechanism of action is the reversible inhibition of the **Naⁱ-Kⁱ-2Cl⁻ symporter (NKCC2)** [2] located in the luminal membrane of the **Thick Ascending Limb (TAL)** of the Loop of Henle [4]. By blocking this transporter, it prevents the reabsorption of these electrolytes, leading to a significant increase in the excretion of sodium, chloride, and water [2]. Because the TAL is responsible for reabsorbing ~25% of filtered sodium, loop diuretics are the most efficacious diuretics ("High-ceiling diuretics") [3]. **2. Why Other Options are Incorrect:** * **Option B (Aldosterone antagonism):** This describes **Spironolactone** and Eplerenone. These are potassium-sparing diuretics that act on the mineralocorticoid receptors in the collecting ducts. * **Option C (Inhibition of Na-Cl symporter):** This is the mechanism of **Thiazide diuretics** (e.g., Hydrochlorothiazide), which act specifically on the **Distal Convoluted Tubule (DCT)** [3]. * **Option D (Carbonic anhydrase inhibition):** This describes **Acetazolamide**, which acts primarily in the **Proximal Convoluted Tubule (PCT)** [5]. **3. High-Yield Clinical Pearls for NEET-PG:** * **Electrolyte Changes:** Furosemide causes **Hypokalemia**, **Hypomagnesemia**, and notably **Hypocalcemia** (unlike Thiazides, which cause hypercalcemia) [4]. "Loop loses calcium." * **Drug of Choice:** It is the treatment of choice for **Acute Pulmonary Edema** due to its rapid onset and additional vasodilator effect. * **Adverse Effects:** Watch for **Ototoxicity** (especially when combined with aminoglycosides), Hyperuricemia (can precipitate Gout), and Sulfa-allergy cross-reactivity [1]. * **Site of Action:** Always remember—Loop diuretics act on the **Thick Ascending Limb** [2].

Q: Acetazolamide side effects include all except:

Diarrhea. **Explanation:** Acetazolamide is a **Carbonic Anhydrase Inhibitor** that acts primarily at the proximal convoluted tubule (PCT). It inhibits the enzyme carbonic anhydrase, leading to the excretion of sodium, potassium, and bicarbonate. **Why "Diarrhea" is the correct answer:** Diarrhea is not a recognized side effect of Acetazolamide. In fact, the most common gastrointestinal side effect associated with its use is **nausea or anorexia**, but it does not typically cause increased bowel motility or diarrhea. **Analysis of Incorrect Options:** * **Hypokalemia (Option A):** By increasing the delivery of sodium and water to the distal tubule, Acetazolamide promotes potassium secretion into the urine. This is a classic side effect of most diuretics (except potassium-sparing ones). * **Drowsiness (Option B):** Acetazolamide can cause Central Nervous System (CNS) depression, leading to sedation, fatigue, and drowsiness, especially in patients with hepatic impairment. * **Paresthesia (Option C):** This is a very common and high-yield side effect. Patients often report "pins and needles" sensations in the extremities and face due to the metabolic acidosis and electrolyte shifts induced by the drug. **High-Yield Clinical Pearls for NEET-PG:** * **Metabolic Acidosis:** Acetazolamide causes **Hyperchloremic Metabolic Acidosis** (due to bicarbonate loss). * **Therapeutic Uses:** Glaucoma (decreases aqueous humor), Altitude Sickness (prophylaxis), and Urinary Alkalization (to excrete acidic drugs like aspirin). * **Contraindication:** Avoid in patients with **Liver Cirrhosis**, as it decreases ammonia excretion, potentially precipitating hepatic coma. * **Renal Stones:** It can cause calcium phosphate stones because calcium is less soluble in alkaline urine.

Q: Which of the following is used for prophylaxis of acute mountain sickness?

Acetazolamide. **Explanation:** **Acetazolamide** is the drug of choice for the prophylaxis of **Acute Mountain Sickness (AMS)**. **Mechanism of Action:** Acetazolamide is a **Carbonic Anhydrase Inhibitor**. At high altitudes, the low partial pressure of oxygen leads to hyperventilation, causing respiratory alkalosis. This alkalosis inhibits the respiratory center, preventing further compensatory breathing. Acetazolamide works by: 1. Inhibiting carbonic anhydrase in the proximal convoluted tubule, leading to **bicarbonate diuresis**. 2. Inducing a mild **metabolic acidosis**, which counteracts the respiratory alkalosis. 3. This acidification of the blood stimulates the central chemoreceptors, increasing the respiratory drive and improving oxygenation (speeding up acclimatization). **Why other options are incorrect:** * **Furosemide (Loop Diuretic):** While it may be used in the treatment of High-Altitude Pulmonary Edema (HAPE) to reduce lung congestion, it has no role in the prophylaxis of AMS and can cause severe dehydration. * **Spironolactone (Aldosterone Antagonist):** It is a potassium-sparing diuretic used in heart failure and cirrhosis; it does not affect the acid-base balance required to stimulate respiration at high altitudes. **High-Yield Clinical Pearls for NEET-PG:** * **Prophylaxis Dose:** Start Acetazolamide 125–250 mg twice daily, 24 hours before ascent. * **Side Effects:** Paresthesia (tingling in extremities) and a metallic taste when consuming carbonated beverages. * **Contraindication:** Avoid in patients with severe **sulfonamide allergy**. * **Treatment of Choice for HAPE:** Nifedipine (decreases pulmonary artery pressure). * **Treatment of Choice for HACE (High-Altitude Cerebral Edema):** Dexamethasone.

Q: Intravenous (IV) Mannitol is used in which of the following conditions?

Angle closure glaucoma. **Explanation:** **Angle Closure Glaucoma (Correct Answer):** IV Mannitol is a potent **hyperosmotic agent** used as a first-line emergency treatment for Acute Angle Closure Glaucoma (AACG). It works by increasing the plasma osmolarity relative to the vitreous humor. This creates an osmotic gradient that draws water out of the vitreous into the intravascular space, leading to a rapid reduction in vitreous volume and a subsequent drop in Intraocular Pressure (IOP). This "dehydration" of the vitreous helps deepen the anterior chamber and break the pupillary block. **Analysis of Incorrect Options:** * **Central Retinal Artery Occlusion (CRAO):** While reducing IOP is a goal in CRAO to improve perfusion, the primary emergency management involves ocular massage, anterior chamber paracentesis, or inhaled carbogen. Mannitol is not the standard of care here. * **Congestive Heart Failure (CHF) & Pulmonary Edema:** These are **absolute contraindications** for Mannitol. Mannitol initially causes a rapid expansion of extracellular fluid volume (drawing fluid from cells into the blood). In patients with CHF or pulmonary edema, this sudden increase in preload can lead to acute cardiac decompensation and worsen respiratory distress. **NEET-PG High-Yield Pearls:** * **Dose:** 1.5–2.0 g/kg body weight as a 20% solution, infused over 30–60 minutes. * **Mechanism:** Vitreous dehydration (Osmotic effect). * **Side Effects:** Headache (most common due to cerebral dehydration), nausea, and electrolyte imbalances. * **Contraindications:** Renal failure (anuria), severe dehydration, and active intracranial bleeding (except during craniotomy). * **Clinical Tip:** Always check the bottle for crystals; if present, warm the bottle to redissolve them before administration.

Question 1

A new diuretic is being studied in human volunteers. Compared with placebo, the new drug increases urine volume, decreases urinary Ca2+, increases body pH, and decreases serum K+. If this new drug has a similar mechanism of action to an established diuretic, it probably what?

Accepted Answer

Blocks the NaCl cotransporter in the distal convoluted tubule.

Answer

Blocks aldosterone receptors in the collecting tubule.

Answer

Inhibits carbonic anhydrase in the proximal convoluted tubule.

Answer

Inhibits the Na/K/2Cl cotransporter in the thick ascending limb.

Question 2

Mannitol when given intravenously causes which of the following changes?

Accepted Answer

Decrease in blood viscosity

Answer

Increase in blood viscosity

Answer

Increase in GFR

Answer

Increase in ICT

Question 3

Acetazolamide is administered to a glaucoma patient. Given that this drug inhibits carbonic anhydrase in the renal proximal tubule, which of the following substances will be excreted at a lower rate?

Accepted Answer

NH4+

Answer

Na+

Answer

H2O

Answer

HCO3-

Question 4

A 68-year-old woman presents for a routine check-up with occasional ankle swelling. Her serum potassium is 3.5 mEq/L. Which of the following diuretics would be most appropriate for this patient, considering the need to avoid unnecessary potassium losses?

Accepted Answer

Amiloride

Answer

Furosemide

Answer

Hydrochlorothiazide

Answer

Spironolactone

Question 5

A 47-year-old HIV-positive man presents with weakness, HIV nephropathy, and adrenal insufficiency. He is taking trimethoprim-sulfamethoxazole for PCP prophylaxis and triple-agent antiretroviral treatment. He was recently started on spironolactone for ascites due to alcoholic liver disease. Physical examination reveals normal vital signs, but his muscles are diffusely weak. Frequent extrasystoles are noted. He has mild ascites and 1+ peripheral edema. Laboratory studies show a serum creatinine of 2.5 mg/dL with a potassium value of 7.3 mEq/L. ECG shows peaking of the T-waves and QRS widening to 0.14 seconds. Once the patient is stabilized and the T-waves have normalized, it is important to review the potential causes of his hyperkalemia and to take steps to prevent this from happening again. As you consider the pathophysiology of each factor, which of the following statements is true?

Accepted Answer

Spironolactone, a diuretic for ascites in cirrhosis, acts as a competitive aldosterone inhibitor at the collecting duct, decreasing potassium excretion and causing hyperkalemia.

Answer

Trimethoprim-sulfamethoxazole, used for Pneumocystis infection prophylaxis, causes hypokalemia and therefore would have prevented this patient's presentation.

Answer

The patient likely had pseudo-hyperkalemia due to hemolysis caused by using a small needle and rough specimen handling, leading to potassium release into the serum.

Answer

Once hospitalized, the patient may receive heparin for DVT prophylaxis, which would help ameliorate hyperkalemia in the ensuing days.

Question 6

Acetazolamide acts at which part of the nephron?

Accepted Answer

Proximal Convoluted Tubule (PCT)

Answer

Distal Convoluted Tubule (DCT)

Answer

Ascending loop of Henle

Answer

Descending loop of Henle

Question 7

What is the mechanism of action of furosemide as a diuretic?

Accepted Answer

Inhibition of Na-K-Cl ion symporter

Answer

Aldosterone antagonism

Answer

Inhibition of Na-Cl symporter in distal tubules

Answer

Carbonic anhydrase inhibition

Question 8

Acetazolamide side effects include all except:

Accepted Answer

Diarrhea

Answer

Hypokalemia

Answer

Drowsiness

Answer

Paresthesia

Question 9

Which of the following is used for prophylaxis of acute mountain sickness?

Accepted Answer

Acetazolamide

Answer

Furosemide

Answer

Spironolactone

Answer

All of the above

Question 10

Intravenous (IV) Mannitol is used in which of the following conditions?

Accepted Answer

Angle closure glaucoma

Answer

Central Retinal Artery Occlusion (CRAO)

Answer

Congestive Heart Failure

Answer

Pulmonary edema

Diuretics — MCQs

Diuretics — MCQs

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