Pharm 101: Spironolactone

Class

Potassium-sparing diuretic


Pharmacodynamics
  • Synthetic steroid
  • Competitive antagonist to aldosterone at the mineralocorticoid receptor
    • Reduces K secretion –> reduces Na absorption in collecting duct
    • Also inhibits H secretion in parallel

Pharmacokinetics
  • Slow onset and offset of effect
  • Hepatic metabolism to active metabolites canrenone and 7-alpha-spirolactone (long half lives of 12-20 hours)
  • Duration of action 24-48 hours

Clinical uses
  • Primary hyperaldosteronism
  • Secondary hyperaldosteronism:
    • CCF
    • Cirrhosis
    • Nephrotic syndrome

Adverse effects
  • Hyperkalaemia
  • Hyperchloraemic metabolic acidosis:
    • Due to inhibition of H secretion in parallel with K secretion
  • Gynecomastia:
    • Potent inhibitor of androgen receptor

Precautions/contraindications
  • Potassium supplements
  • Dose adjustment in liver failure
  • NSAIDs:
    • Action of aldosterone antagonists depend on renal prostaglandin production

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MBBS (UWA) CCPU Emergency Medicine Trainee with interests in medical education, ECG interpretation, and the use of point-of-care ultrasound in the undifferentiated patient. Co-author of the LITFL ECG Library | Twitter

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