Adrenal replacement (Addison's / CAH)
also: hydrocortisone · fludrocortisone · sick day rules · adrenal crisis · steroid replacement
Overview
Physiological replacement in adrenal insufficiency — glucocorticoid (hydrocortisone) plus, in PRIMARY insufficiency, mineralocorticoid (fludrocortisone). The sick-day rules and the adrenal-crisis response are core exam content.
Mechanism
Hydrocortisone replaces cortisol (glucocorticoid). Fludrocortisone is a potent mineralocorticoid replacing aldosterone → Na⁺ retention, K⁺ excretion (needed only in PRIMARY insufficiency — in secondary, the aldosterone axis is preserved).
Indications
- Primary adrenal insufficiency (Addison's) — hydrocortisone + fludrocortisone
- Secondary (pituitary) insufficiency — hydrocortisone only (aldosterone intact)
- Congenital adrenal hyperplasia
- Adrenal (Addisonian) crisis
The agents
oral, divided — most in the morning
Mimics circadian cortisol; IM/IV for crisis.
oral OD
ONLY in primary insufficiency; titrate to BP/postural drop/K⁺/renin.
Adverse effects
Shock, hypotension, hypoglycaemia, ↓Na/↑K → IM/IV hydrocortisone 100 mg + IV fluids immediately.
Cautions & contraindications
Adrenal crisis — NEVER omit; carry a steroid card.
Stress raises cortisol need → crisis if not covered.
Interactions
- Enzyme inducers (rifampicin, phenytoin) ↑hydrocortisone clearance → may need higher dose
Monitoring & kinetics
BP + postural drop, U&E (Na/K), weight; sick-day-rule education + steroid card + emergency IM hydrocortisone kit
Oral replacement; IM/IV hydrocortisone for crisis. Sick-day rules: DOUBLE the glucocorticoid (fludrocortisone unchanged).
Source: BNF — Corticosteroids / replacement · CKS — Addison's disease