Paper I
2013 April (2010 Scheme) · 40 marks · 180 min

Question

Classify diuretic agents. Describe the mechanism of action, uses and adverse effects of furosemide. (2+2+1+1=6)

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Answer

Classification of diuretics

  • High-efficacy (loop) diuretics: Furosemide, Bumetanide, Torsemide
  • Medium-efficacy (thiazide/thiazide-like): Hydrochlorothiazide, Chlorthalidone, Metolazone
  • Weak/adjunctive:
    • Carbonic anhydrase inhibitors — Acetazolamide
    • Potassium-sparing — Spironolactone, Amiloride, Triamterene
    • Osmotic diuretics — Mannitol

Mechanism of action of furosemide

  • Acts on the thick ascending limb of the loop of Henle
  • Inhibits the Na⁺-K⁺-2Cl⁻ (NKCC2) cotransporter on the luminal membrane
  • Abolishes the medullary concentration gradient, causing marked natriuresis, kaliuresis, and loss of the ability to concentrate/dilute urine
  • Also increases renal blood flow and has some venodilator action (useful in acute pulmonary oedema)

Uses

  • Acute pulmonary oedema / left ventricular failure
  • Chronic congestive cardiac failure
  • Oedema of hepatic and renal origin (nephrotic syndrome)
  • Acute renal failure (to maintain urine flow)
  • Hypertension (especially with renal impairment)
  • Hypercalcaemia, forced diuresis in poisoning

Adverse effects

  • Hypokalaemia, hyponatraemia, hypomagnesaemia
  • Hypotension, dehydration
  • Ototoxicity (especially with rapid IV injection or with aminoglycosides)
  • Hyperuricaemia (may precipitate gout)
  • Hyperglycaemia
  • Metabolic alkalosis

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