Mannitol is an example of?

AIIMS Delhi NO - 2017

Pharmacology

Easy

Appeared in: AIIMS Delhi NO - 2017

Explanation

Mannitol is classified as an osmotic diuretic.
It is a sugar alcohol that is freely filtered by the glomerulus but poorly reabsorbed by the renal tubules.
This increases the osmolality (solute concentration) of the tubular fluid, which draws water from the body into the tubules via osmosis, leading to increased urine output.
Its primary uses are to reduce acutely elevated intracranial pressure (cerebral edema) and intraocular pressure (acute glaucoma).

Option A: Loop diuretics, such as furosemide, act by inhibiting the sodium-potassium-chloride cotransporter in the thick ascending limb of the loop of Henle. This is a different mechanism and site of action compared to mannitol.
Option C: Potassium-sparing diuretics, like spironolactone, act on the distal tubules and collecting ducts to block the action of aldosterone or inhibit sodium channels, thus preventing potassium excretion. Mannitol does not have this effect.
Option D: Carbonic anhydrase inhibitors, such as acetazolamide, work by blocking the enzyme carbonic anhydrase in the proximal convoluted tubules, which reduces bicarbonate reabsorption. Mannitol's mechanism is osmotic, not enzymatic.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Pharmacological classification of diuretics as background academic context rather than a clinical decision trigger.
Nurses must administer IV mannitol using a filter needle, as the solution can crystallize at room temperature, which could lead to infusion of harmful particles.
When administering mannitol for cerebral edema, a key nursing responsibility is to monitor the patient's neurological status, serum osmolality, and electrolytes to assess effectiveness and prevent complications like dehydration or electrolyte imbalance.
What if? If a patient receiving mannitol develops crackles in the lungs and shortness of breath, the infusion should be stopped immediately. This is because mannitol initially expands the extracellular fluid volume, which can precipitate or worsen heart failure and pulmonary edema in susceptible individuals.

How to Approach the Question

This is a factual recall question from pharmacology that tests your knowledge of drug classifications.
Identify the drug in the question stem: 'Mannitol'.
Recall the major classes of diuretics: loop, osmotic, potassium-sparing, and thiazide/carbonic anhydrase inhibitors.
Mentally place Mannitol into its correct category. Its mechanism of increasing osmotic pressure is the key defining feature.
Evaluate the given options. 'Osmotic diuretic' directly describes Mannitol's class and mechanism.
Eliminate the other options by associating them with their prototype drugs (e.g., Loop -> Furosemide; Potassium-sparing -> Spironolactone; Carbonic anhydrase inhibitor -> Acetazolamide).

Concept Tested & Keywords

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