# Diuretics for NEET PG Pharmacology: Loop, Thiazide, Potassium-Sparing, Acetazolamide, Mannitol and Tolvaptan

Source: https://tracknation.in/story/diuretics-for-neet-pg-pharmacology-loop-thiazide-potassium-sparing-acetazolamide-mannitol-and-tolvaptan (TrackNation — free UPSC notes with PYQs)

> NEET PG Pharmacology: diuretics by site of action with their effects on potassium, calcium, sodium, glucose and uric acid; furosemide ototoxicity, thiazide and lithium, spironolactone and gynaecomastia, acetazolamide for glaucoma and altitude, mannitol for raised ICP, tolvaptan and osmotic demyelination, and ICMR hypertension and heart-failure use, with a diagram, hooks, vignette MCQs and cards.

## Start Here

🎯 **Exam priority: High.** *Expect: which diuretic raises calcium or potassium, a deaf patient on furosemide and gentamicin,
lithium toxicity after a thiazide, gynaecomastia on spironolactone, acetazolamide on a trek, and mannitol for raised ICP.*

Indian use follows the **ICMR Hypertension (May 2026)** and **Heart Failure (January 2026)** workflows.

## Where Each Diuretic Acts

*Diuretic classes: site or mechanism and effect on blood potassium and calcium, from the drugs' prescribing labels. Drawn by TrackNation.*

- **Loop** (furosemide, torsemide): block the Na-K-2Cl carrier in the thick ascending limb; that site makes them the most
powerful. Lower K, Ca and Mg; raise uric acid.

- **Thiazide** (HCTZ) and **thiazide-like** (chlorthalidone, indapamide): distal tubule. Lower K, Na and Mg;
**reduce urinary calcium** (serum Ca may rise slightly; marked hypercalcaemia suggests hidden hyperparathyroidism); raise glucose and
uric acid.

- **Potassium-sparing**: amiloride blocks Na reabsorption in the distal tubule and collecting duct; spironolactone and
eplerenone block aldosterone. All other diuretics cause significant potassium loss.

- **Acetazolamide** inhibits carbonic anhydrase: bicarbonate, Na, water and K are lost in alkaline urine, leaving acidosis.

- **Mannitol** raises the osmolarity of the filtrate. **Tolvaptan** blocks vasopressin V2 receptors.

## Uses and Cautions

| **Drug**

 | **Main uses (label / ICMR)**

 | **Key cautions (label)**

 |
| Furosemide

 | Oedema; IV decongestion in heart failure (ICMR)

 | Anuria; ototoxicity (fast IV, high dose, renal failure, aminoglycosides); sulfonamide allergy; hepatic coma

 |
| Chlorthalidone 12.5–25 mg, HCTZ 12.5 mg

 | Hypertension (ICMR)

 | Contraindicated: pregnancy, gout; low Na, low K, high Ca, glucose intolerance; angle-closure glaucoma

 |
| Indapamide

 | Hypertension

 | Severe hyponatraemia with hypokalaemia, mostly in elderly women

 |
| Spironolactone

 | Heart failure (ICMR: with ARNI), cirrhotic or nephrotic oedema, primary hyperaldosteronism

 | Hyperkalaemia, Addison's disease; gynaecomastia (about 9% of men in RALES)

 |
| Eplerenone

 | Heart failure after MI; hypertension

 | Check K before and during; not with strong CYP3A inhibitors (ketoconazole)

 |
| Amiloride

 | Added to thiazide or other potassium-losing diuretics in heart failure or hypertension

 | Hyperkalaemia (about 10%); not if K > 5.5

 |
| Acetazolamide

 | Glaucoma, epilepsy, acute mountain sickness

 | Low Na or K, cirrhosis (hepatic encephalopathy), hyperchloraemic acidosis

 |
| Mannitol

 | Raised intracranial or intraocular pressure (0.25 g/kg every 6–8 h for ICP)

 | Anuria, severe hypovolaemia, pulmonary congestion or oedema

 |
| Tolvaptan

 | Hypervolaemic or euvolaemic hyponatraemia, including SIADH

 | Start in hospital; Na rise > 12 mEq/L in 24 h → osmotic demyelination; not for ADPKD

 |

Hypertension (ICMR): a CCB or a thiazide/thiazide-like diuretic joins telmisartan in the stepwise protocol. Heart failure (ICMR): decongest with
IV furosemide, then start ARNI and spironolactone.

## Interactions

- **Lithium**: diuretics reduce its renal clearance → lithium toxicity.

- **Aminoglycosides**: furosemide adds to their ototoxicity, especially with poor kidneys.

- **Digoxin**: diuretic-induced hypokalaemia worsens digoxin's effect on the heart.

- **Potassium-sparing drugs with ACE inhibitors, ARBs or poor kidneys**: hyperkalaemia; spironolactone is never combined
with eplerenone.

## Traps the Examiner Sets

- Calcium: loop lowers it, thiazide keeps it in (urinary Ca falls).

- Potassium: only the potassium-sparing group raises it.

- Acetazolamide makes the urine alkaline and the blood acidic.

- Mannitol is wrong in anuria and pulmonary oedema.

- Correct sodium no faster than 12 mEq/L in 24 hours with tolvaptan.

## Memory Hooks & Shortcuts

*Shortcuts to lock in this article's numbers and lists. Each one only re-packages facts proven above.*

- 🧠 **Loops Lose calcium; Thiazides Take it back** — loop lowers serum Ca; thiazide reduces urinary Ca

- 🧠 **Thiazide raises GUC: Glucose, Uric acid, Calcium** — hyperglycaemia, hyperuricaemia, slight hypercalcaemia

- 🧠 **Spiro Swells the chest** — gynaecomastia

- 🧠 **Acetazolamide: Alkaline urine, Acid blood, Altitude** — three A's

- 🧠 **Mannitol Must have urine** — contraindicated in anuria

- 🧠 **Tolvaptan: Twelve is the limit** — do not raise sodium more than 12 mEq/L in 24 hours

- 🧠 **Lithium hates diuretics** — toxicity from reduced clearance

## Rapid-Revision Cards

- Na-K-2Cl, thick ascending limb; most efficacious.

- ↓K, ↓Ca, ↓Mg, ↑uric acid.

- Fast IV, high dose, renal failure, aminoglycosides.

- Anuria; sulfa allergy; hepatic coma.

- Distal tubule.

- ↓K, ↓Na, ↓Mg, ↓urinary Ca, ↑glucose, ↑uric acid.

- Acute myopia, angle-closure glaucoma.

- Chlorthalidone 12.5–25 mg; HCTZ 12.5 mg.

- Pregnancy, gout.

- Severe hyponatraemia + hypokalaemia in elderly women.

- Lithium toxicity.

- Distal Na reabsorption block; ~10% hyperkalaemia; not if K > 5.5.

- HF, cirrhotic/nephrotic oedema, hyperaldosteronism.

- Hyperkalaemia, Addison's, with eplerenone; gynaecomastia.

- Check K; no strong CYP3A inhibitors.

- Carbonic anhydrase; glaucoma, epilepsy, altitude.

- Alkaline urine, metabolic acidosis.

- Cirrhosis (encephalopathy), low Na/K.

- Osmotic; ICP 0.25 g/kg every 6–8 h; also IOP.

- Anuria, hypovolaemia, pulmonary oedema.

- V2 antagonist; hyponatraemia incl. SIADH.

- Start in hospital; ≤ 12 mEq/L rise per 24 h.

- IV furosemide, then ARNI + spironolactone.

## Sources

*Facts in this article were checked against these documents.*

- Standard Treatment Workflows: Hypertension in Adults (May 2026); Heart Failure (January 2026) — Indian Council of Medical Research / Department of Health Research, MoHFW, 2026

- Medications for Hypertension — MSD Manual Professional Version, accessed November 2026 (link)

- Prescribing labels: furosemide, torsemide, hydrochlorothiazide, chlorthalidone, indapamide, amiloride, Aldactone, Inspra, acetazolamide, Osmitrol, Samsca — DailyMed, US National Library of Medicine, current labels, accessed November 2026 (link)

- Competency Based Undergraduate Curriculum, Pharmacology — National Medical Commission, 2024

## Test Yourself: Practice Questions

Twenty-four questions in NEET PG style, most of them clinical vignettes.

## Practice Questions (NEET PG pattern)

*Original questions written in the style of the exam: +4 for a correct answer, −1 for a wrong one. Every answer
was checked against the sources listed above. NEET PG papers are not published by NBEMS, so these are not past-paper questions.*

**Q1.** Furosemide acts mainly by inhibiting

- (a) the Na-K-2Cl carrier in the thick ascending limb

- (b) carbonic anhydrase

- (c) the aldosterone receptor

- (d) the vasopressin V2 receptor

**Answer: (a)** — Loop diuretics act in the thick ascending limb (torsemide label); the site explains their high efficacy (furosemide label).

**Q2.** A patient on IV gentamicin with renal impairment is given high-dose IV furosemide and develops hearing loss. The reason is

- (a) gentamicin causes hypokalaemia

- (b) furosemide causes hypercalcaemia

- (c) an allergic reaction

- (d) furosemide increases aminoglycoside ototoxicity

**Answer: (d)** — Furosemide ototoxicity: rapid injection, high doses, renal failure and aminoglycosides.

**Q3.** Which diuretic class decreases urinary calcium excretion?

- (a) carbonic anhydrase inhibitor

- (b) thiazide

- (c) loop

- (d) osmotic

**Answer: (b)** — Thiazides decrease urinary calcium excretion; loop diuretics lower serum calcium.

**Q4.** A man on lithium for bipolar disorder starts hydrochlorothiazide for hypertension and becomes tremulous and confused. The cause is

- (a) lithium inducing thiazide metabolism

- (b) reduced renal clearance of lithium causing toxicity

- (c) hypercalcaemia alone

- (d) thiazide-induced hypoglycaemia

**Answer: (b)** — Diuretics reduce lithium clearance and add a high risk of lithium toxicity.

**Q5.** A 60-year-old with gout needs antihypertensive treatment. Per the ICMR table, which class is contraindicated?

- (a) ARBs

- (b) Thiazide/thiazide-like diuretics

- (c) ACE inhibitors

- (d) Calcium-channel blockers

**Answer: (b)** — ICMR lists pregnancy and gout as contraindications to chlorthalidone and HCTZ.

**Q6.** A prediabetic man's fasting glucose rises after starting a thiazide. The label explanation is

- (a) thiazides cause insulin overdose

- (b) thiazides stimulate glucagon only

- (c) thiazides can cause hyperglycaemia and unmask latent diabetes

- (d) it is unrelated

**Answer: (c)** — Hyperglycaemia may occur; latent diabetes may become manifest.

**Q7.** An elderly woman on indapamide is brought in confused. The electrolyte picture to expect is

- (a) severe hyponatraemia with hypokalaemia

- (b) hypercalcaemia only

- (c) normal electrolytes

- (d) hypernatraemia with hyperkalaemia

**Answer: (a)** — Indapamide label: severe hyponatraemia with hypokalaemia, mainly in elderly females.

**Q8.** Soon after starting hydrochlorothiazide, a woman develops sudden blurred vision and eye pain. Suspect

- (a) cataract

- (b) retinal detachment from hypokalaemia

- (c) acute myopia with secondary angle-closure glaucoma

- (d) optic neuritis from gout

**Answer: (c)** — HCTZ, a sulfonamide, can cause an idiosyncratic acute transient myopia and acute angle-closure glaucoma, typically within hours to weeks.

**Q9.** A man with heart failure on spironolactone develops tender breast enlargement. The label says

- (a) this is from furosemide

- (b) it is due to digoxin only

- (c) it means hyperkalaemia

- (d) spironolactone causes gynaecomastia (about 9% of men in RALES)

**Answer: (d)** — Aldactone warning: gynaecomastia.

**Q10.** Spironolactone is contraindicated in

- (a) primary hyperaldosteronism

- (b) cirrhotic ascites

- (c) hypokalaemia

- (d) hyperkalaemia and Addison's disease

**Answer: (d)** — Contraindications: hyperkalaemia, Addison's disease, use with eplerenone. Hyperaldosteronism and cirrhotic oedema are indications.

**Q11.** A patient on amiloride and an ACE inhibitor has serum potassium 6.1 mEq/L. Amiloride

- (a) lowers potassium

- (b) is safe with any potassium

- (c) should be doubled

- (d) should not be used when potassium exceeds 5.5 mEq/L

**Answer: (d)** — Hyperkalaemia occurs in about 10% with amiloride; contraindicated if K > 5.5.

**Q12.** Which diuretic does not cause significant potassium loss?

- (a) Spironolactone

- (b) Hydrochlorothiazide

- (c) Furosemide

- (d) Acetazolamide

**Answer: (a)** — MSD: all diuretics except potassium-sparing distal diuretics cause significant potassium loss.

**Q13.** A patient with heart failure after MI is on eplerenone and is prescribed ketoconazole. The label says

- (a) no interaction

- (b) switch to spironolactone plus eplerenone

- (c) double eplerenone

- (d) eplerenone is contraindicated with strong CYP3A inhibitors

**Answer: (d)** — Contraindicated with strong CYP3A inhibitors such as ketoconazole; check potassium before and during treatment.

**Q14.** A trekker planning rapid ascent to high altitude asks for prophylaxis. A suitable drug is

- (a) mannitol

- (b) acetazolamide

- (c) spironolactone

- (d) furosemide

**Answer: (b)** — Acetazolamide prevents or lessens acute mountain sickness in rapid ascent.

**Q15.** On acetazolamide, the urine and blood change as follows:

- (a) acid urine with acidosis

- (b) alkaline urine with metabolic acidosis

- (c) no change in pH

- (d) acid urine with alkalosis

**Answer: (b)** — Bicarbonate (with Na, water, K) is lost, alkalinising the urine; the acidotic state can be corrected with bicarbonate.

**Q16.** Acetazolamide is contraindicated in a patient with cirrhosis because of the risk of

- (a) hepatic encephalopathy

- (b) ototoxicity

- (c) gynaecomastia

- (d) hyperkalaemia

**Answer: (a)** — Acetazolamide label.

**Q17.** A head-injury patient has raised intracranial pressure. Mannitol is given at

- (a) 0.25 g/kg IV every 6–8 hours

- (b) 0.25 mg/kg SC

- (c) 5 g/kg orally once

- (d) 1 g IV once weekly

**Answer: (a)** — Osmitrol: 0.25 g/kg infused over 30 minutes every 6–8 hours for raised ICP.

**Q18.** Mannitol is contraindicated in a patient with

- (a) normal renal function

- (b) raised intraocular pressure

- (c) anuria or pulmonary oedema

- (d) cerebral oedema

**Answer: (c)** — Contraindications: anuria, severe hypovolaemia, severe pulmonary congestion or oedema, active intracranial bleeding (except craniotomy).

**Q19.** A patient with SIADH and sodium 118 mEq/L is started on tolvaptan; next day sodium is 133. The danger is

- (a) osmotic demyelination from too-rapid correction

- (b) gynaecomastia

- (c) ototoxicity

- (d) hyperkalaemia

**Answer: (a)** — Correction > 12 mEq/L in 24 hours can cause osmotic demyelination; start in hospital with sodium monitoring.

**Q20.** Tolvaptan acts as

- (a) a loop diuretic

- (b) an aldosterone antagonist

- (c) a selective vasopressin V2-receptor antagonist

- (d) a carbonic anhydrase inhibitor

**Answer: (c)** — Samsca label.

**Q21.** A man with acute heart failure and pulmonary congestion arrives at a district hospital. ICMR's first diuretic step is

- (a) acetazolamide

- (b) decongest with IV furosemide

- (c) IV mannitol

- (d) oral spironolactone alone

**Answer: (b)** — ICMR HF workflow: decongest with IV furosemide; then start ARNI and spironolactone.

**Q22.** An elderly woman with heart failure on digoxin is started on furosemide without potassium monitoring. The risk is

- (a) hyperkalaemia blocking digoxin

- (b) hypercalcaemia

- (c) no interaction

- (d) hypokalaemia exaggerating digoxin's cardiac effects

**Answer: (d)** — Furosemide causes hypokalaemia; digitalis exaggerates its effects on the heart.

**Q23.** A patient on a thiazide has a serum calcium of 12.5 mg/dL (markedly raised). The label suggests

- (a) adding calcium

- (b) it is always due to the thiazide alone

- (c) doubling the thiazide

- (d) looking for hidden hyperparathyroidism

**Answer: (d)** — Thiazides cause only slight rises; marked hypercalcaemia may indicate hidden hyperparathyroidism.

**Q24.** A patient with sulfonamide allergy is due to start furosemide. The label warns

- (a) they may also be allergic to furosemide

- (b) there is no cross-reactivity

- (c) furosemide is a penicillin

- (d) give it IV to avoid allergy

**Answer: (a)** — Patients allergic to sulfonamides may also be allergic to furosemide.

### Active Recall

From memory: for each diuretic class give its site or mechanism, its effect on potassium, calcium and sodium, its main uses and its key adverse effects and interactions (lithium, aminoglycosides, digoxin).