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Spironolactone

Class
Indications
Administration/Absorption
  • Oral
    • Fairly rapidly absorbed from the gastrointestinal tract
    • Food increases the bioavailability of unmetabolized spironolactone by almost 100%.
Dosage

Distribution
  • Spironolactone and its metabolites are more than 90% bound to plasma proteins.
Mechanism
  • Spironolactone is a synthetic 17-lactone steroid
  • Renal competitive aldosterone antagonist
  • On its own, spironolactone is only a weak diuretic
    • It may be given alone or with other diuretic agents which act more proximally in the renal tubule
  • Due to its anti-androgen effect, it can also be used to treat hirsutism
    • Common component in hormone therapy for male-to-female transgendered people
  • Spironolactone inhibits the effect of aldosterone by competing for intracellular aldosterone receptor in the distal tubule cells
    • Antagonises a cytoplasmic mineralocorticoid receptor responsible for enhancing expression of Na+, K+-ATPase and the Na+ channel involved in a Na+ K+ transport in the distal tubule
    • This increases the secretion of water and sodium, while decreasing the excretion of potassium
  • Spironolactone has a fairly slow onset of action, taking several days to develop and similarly the effect diminishes slowly.
Excretion
  • Half-life 10 mins
  • Rapidly and extensively metabolized
    • Divided into two main routes
      • those in which the sulfur moiety is retained
      • those in which the sulfur moiety is removed by dethioacetylation.
    • Transformed to a reactive metabolite
      • Can inactivate adrenal and testicular cytochrome P450 enzymes
      • Has anti-androgenic activity.
  • Excreted primarily in the urine and secondarily in bile
Side effects
  • Oral LD50 of spironolactone is greater than 1,000 mg/kg in mice, rats, and rabbits
  • Acute overdosage of spironolactone may be manifested by:
    • Drowsiness, mental confusion, maculopapular or erythematous rash, nausea, vomiting, dizziness, or diarrhea
  • Spironolactone has been shown to be a tumorigen in chronic toxicity studies in rats.
Interactions

Contraindications

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