Loop Diuretics

Mechanism of Action

  • Inhibits water reabsorption in the nephron by blocking the Na-K-Cl cotransporter (NKCC2) in the thick ascending limb of the loop of Henle


  • Pulmonary oedema due to left ventricular failure; thiazide-resistant oedema in patients with chronic heart failure; patients with treatment refractory hypertension (or in patients with poor renal function)


  • Hypovolaemic/hypotensive patients- ideally correct prior to treatment
  • Monitor electrolytes during treatment
  • Caution in diabetes (may worsen diabetes- though less commonly than thiazides); same with gout
  • In patients with enlarged prostates, loop diuretics may cause urinary retention (make sure an adequate urine outflow before treatment)


  • Severe hypokalaemia/hyponatraemia; anuria;
  • Severe liver disease causing coma/precoma (may precipitate encephalopathy)
  • Renal failure due to neprho-/hepatotoxic drugs

Side effects

  • In high IV doses, can cause tinnitus and deafness
  • GI disturbance, pancreatitis, hepatic encephalopathy
  • Postural hypotension
  • Temporary increase in cholesterol/triglycerides
  • Electrolyte/metabolic disturbance
    • Hyperglycaemia (less common than thiazides)
    • Hyponatraemia; hypokalaemia; hypocalcaemia; hypochloraemia; hypomagesaemia
    • Metabolic alkalosis
    • Hyperuricaemia (gout)
  • Rarely, blood disorders e.g. bone marrow suppression, thrombocytopenia, leucopenia

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