Which of the following is a loop diuretic?

Appeared in: RML PRE 2025

Explanation

Furosemide is classified as a loop diuretic, also known as a high-ceiling diuretic, due to its high potency.
Its primary site of action is the thick ascending limb of the loop of Henle in the kidney's nephron.
Furosemide works by blocking the sodium-potassium-2-chloride (Na⁺-K⁺-2Cl⁻) cotransporter.
This inhibition prevents the reabsorption of a significant amount of sodium and chloride, leading to powerful diuresis (increased urine output).
It is commonly used for rapid fluid removal in conditions like pulmonary edema and congestive heart failure.

Option B: Hydrochlorothiazide is a thiazide diuretic, not a loop diuretic. It is less potent than furosemide.
Option C: Spironolactone is a potassium-sparing diuretic. Its primary function is to promote sodium and water excretion while conserving potassium.
Option D: Acetazolamide is a carbonic anhydrase inhibitor. It is a weak diuretic and has different primary indications.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Classification and Mechanism of Action of Diuretics as background academic context rather than a clinical decision trigger.
Nurses must closely monitor patients on loop diuretics for signs of dehydration and electrolyte imbalances, particularly hypokalemia, which can cause cardiac arrhythmias.
Patient education is critical. Instruct patients to take furosemide in the morning to avoid sleep disruption from nocturia and to report dizziness or lightheadedness, which may indicate orthostatic hypotension.
Daily weight measurement is the most reliable indicator of fluid loss and the effectiveness of diuretic therapy. A weight gain of more than 1 kg (2.2 lbs) in 24 hours should be reported.

How to Approach the Question

First, identify the core of the question, which is asking to classify a specific drug: 'Which...is a loop diuretic?'.
This is a factual recall question from pharmacology. You need to access your knowledge of diuretic drug classes.
Mentally list or recall the main categories of diuretics: loop, thiazide, potassium-sparing, and carbonic anhydrase inhibitors.
Go through each option and try to place it into one of these categories.
Recall that Furosemide (Lasix) is the most common example of a loop diuretic.
Confirm by classifying the other options: Hydrochlorothiazide (thiazide), Spironolactone (potassium-sparing), and Acetazolamide (carbonic anhydrase inhibitor). This confirms Furosemide is the only loop diuretic listed.

Concept Tested & Keywords

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E6 Pharmacology Katzung 16e pp. 423-425, 346-348

E6 Pharmacology Nursing Lilley 11e Part 2 p. 147-149

Practise the full RML PRE 2025

Attempt every question from this paper in a timed mock, then review the full solution for each one.