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
Pharmacology 101
Top 200 drugs
Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Co-creator of the LITFL ECG Library. Twitter: @rob_buttner