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

Indications

• 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)

Cautions

• 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)

Contraindications

• 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