A 35-year-old man presents with weakness, weight loss, hypotension (postural drop 25 mmHg), hyperpigmentation of buccal mucosa and skinfolds, hyponatraemia (Na 128 mEq/L), and hyperkalemia (K 5.9 mEq/L). Short Synacthen test shows basal cortisol 4 μg/dL rising to 8 μg/dL at 30 minutes. ACTH is 980 pg/mL. Which is the correct steroid replacement regimen?
- A Dexamethasone 0.5 mg once daily; fludrocortisone 0.1 mg/day
- B Hydrocortisone 20 mg in morning + 10 mg at noon; fludrocortisone 0.1 mg/day ✓
- C Prednisolone 5 mg + fludrocortisone 0.05 mg/day
- D Hydrocortisone 20 mg once daily only; no mineralocorticoid needed
Explanation
Primary adrenal insufficiency (Addison's disease) requires both glucocorticoid and mineralocorticoid replacement. The standard regimen is hydrocortisone (the most physiological glucocorticoid) given in divided doses mimicking the diurnal cortisol rhythm: 10–20 mg in the morning and 5–10 mg in the early afternoon (total 15–25 mg/day). Fludrocortisone 0.05–0.2 mg/day provides mineralocorticoid replacement to correct hyponatraemia and hyperkalaemia. Dexamethasone lacks mineralocorticoid activity and is not preferred for routine replacement due to over-suppression of the HPA axis.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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