How does fludrocortisone work in the body?
Fludrocortisone is a synthetic corticosteroid with strong mineralocorticoid activity. Its main mechanism is to mimic aldosterone at mineralocorticoid (MC) receptors, which increases sodium reabsorption and promotes potassium and hydrogen ion loss in the kidney’s distal nephron and collecting duct. This leads to:
- Higher blood volume and blood pressure from sodium (and water) retention
- Lower serum potassium from increased potassium excretion
What does it do to electrolytes and blood pressure?
By acting like aldosterone, fludrocortisone shifts renal electrolyte handling:
- Sodium: increases reabsorption → more fluid retention
- Potassium: increases secretion/excretion → hypokalemia risk
- Acid-base effects: increases hydrogen ion excretion → can contribute to metabolic alkalosis
Why does it help in conditions like adrenal insufficiency?
In primary adrenal insufficiency (and related states), the body lacks enough natural aldosterone and cortisol. Fludrocortisone mainly replaces aldosterone’s mineralocorticoid effect, improving circulatory stability by restoring sodium balance and supporting blood pressure.
What about the glucocorticoid effects?
Fludrocortisone also has glucocorticoid activity, but its clinical use often emphasizes the mineralocorticoid effect. In practice, that means its key functional outcomes are changes in fluid balance and electrolytes (rather than primarily anti-inflammatory or immunosuppressive effects).
What patient effects are consistent with its mechanism?
Because its mineralocorticoid action increases sodium retention and potassium loss, common mechanism-related risks include:
- Fluid retention, edema, and higher blood pressure
- Low potassium (hypokalemia)
- Metabolic alkalosis in susceptible patients
Sources
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