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 CCPU (RCE, Biliary, DVT, E-FAST, AAA) Rob is an Emergency Medicine Advanced Trainee based in Melbourne, Australia. He has special interests in medical education, ECG interpretation, and the use of diagnostic and procedural ultrasound in the undifferentiated and unwell patient.

Follow him on twitter: @rob_buttner | ECG Library |

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