Differing glucocorticoid and mineralocorticoid potency between agents
Mnemonic
Equivalent anti-inflammatory doses, and the mineralocorticoid activity that goes with them:
| Steroid | Equivalent dose | Mineralocorticoid effect |
|---|---|---|
| Hydrocortisone | 20 mg | High |
| Prednisolone | 5 mg | Moderate |
| Methylprednisolone | 4 mg | Low |
| Dexamethasone | 0.75 mg | None |
| Fludrocortisone | Very high |
“Hydrocortisone 20, prednisolone 5, dexamethasone 0.75” is the trio worth memorising, and dexamethasone is roughly 25 times as potent as hydrocortisone.
Dexamethasone has no mineralocorticoid activity, which is why it is used where fluid retention would be harmful, in cerebral oedema and croup, and why it cannot be used alone in adrenal insufficiency.
Adrenal suppression follows any course over about 3 weeks, or repeated short courses, and requires tapering rather than abrupt withdrawal, plus sick day rules doubling the dose during intercurrent illness.
Expansion
| Steroid | Equivalent dose | Glucocorticoid | Mineralocorticoid |
|---|---|---|---|
| Hydrocortisone | 20 mg | 1 | 1 |
| Prednisolone | 5 mg | 4 | 0.8 |
| Methylprednisolone | 4 mg | 5 | 0.5 |
| Dexamethasone | 0.75 mg | 25 | ~0 |
| Fludrocortisone | 10 | 125 |
The clinical logic follows the table: hydrocortisone for adrenal replacement because it provides both activities; fludrocortisone added when mineralocorticoid replacement is needed, as in Addison disease; dexamethasone for cerebral oedema and in obstetrics because it lacks fluid-retaining effects and crosses the placenta; prednisolone for most inflammatory conditions.
Adverse effects by duration: short term gives hyperglycaemia, mood change, insomnia and increased appetite; long term gives Cushingoid habitus, osteoporosis, myopathy, skin thinning, cataract, glaucoma, hypertension, infection and adrenal suppression.
Never stop abruptly after more than about 3 weeks of treatment, because of adrenal suppression. Doses should be increased during intercurrent illness or surgery (sick day rules), and every patient on long-term steroids needs a steroid card, bone protection consideration and gastroprotection if on NSAIDs.