Methylprednisolone 20 mg IV is equivalent to hydrocortisone 100 mg IV
The dose-equivalent conversion is approximately 5:1 (hydrocortisone to methylprednisolone), meaning 100 mg of hydrocortisone equals approximately 20 mg of methylprednisolone.
Conversion Rationale
The established glucocorticoid potency ratios show that methylprednisolone has approximately 5 times the anti-inflammatory potency of hydrocortisone 1. This conversion is based on:
- Relative glucocorticoid potency: Methylprednisolone is significantly more potent than hydrocortisone on a milligram-per-milligram basis
- Receptor binding affinity: Research demonstrates good correlation between in vivo EC50 values and relative receptor affinity across corticosteroids 2
- Clinical equivalency: Studies confirm that when given parenterally in equimolar quantities adjusted for potency, these compounds produce equivalent biologic activity 3
Clinical Context for Perioperative/Stress Dosing
The guidelines consistently recommend hydrocortisone 100 mg IV as the standard stress dose for surgery or adrenal crisis 1. If substituting methylprednisolone:
- For major surgery/stress: Methylprednisolone 20 mg IV bolus would theoretically match hydrocortisone 100 mg
- For continuous coverage: The guidelines specify hydrocortisone 200 mg/24h infusion; methylprednisolone equivalent would be approximately 40 mg/24h
Important Caveats
Hydrocortisone remains strongly preferred over methylprednisolone for adrenal insufficiency because:
Mineralocorticoid activity: Hydrocortisone provides essential mineralocorticoid effects that methylprednisolone lacks 1. This is critical in primary adrenal insufficiency where aldosterone deficiency exists.
Guideline preference: All major guidelines (UK Anaesthesia 2020, Endocrine Society 2016, French consensus 2018) specifically recommend hydrocortisone, not methylprednisolone, for stress dosing in adrenal insufficiency 1, 4, 1, 5
Dexamethasone is explicitly contraindicated: The guidelines state dexamethasone "is not adequate as glucocorticoid treatment in patients with primary adrenal insufficiency as it has no mineralocorticoid activity" 1. While methylprednisolone has minimal mineralocorticoid activity (more than dexamethasone but far less than hydrocortisone), this same principle applies.
When Methylprednisolone Might Be Used
The only scenario where methylprednisolone appears in perioperative guidelines is as an alternative in patients on chronic therapeutic steroids (not true adrenal insufficiency): "Alternatively, dexamethasone 6–8 mg intravenously, if used, will suffice for 24 h" 1. Even here, hydrocortisone remains first-line.
Recent comparative data shows no mortality difference between methylprednisolone and hydrocortisone in septic shock 6, but this doesn't address the mineralocorticoid needs in true adrenal insufficiency.
Bottom line: Use the 5:1 conversion (100 mg hydrocortisone = 20 mg methylprednisolone) only when hydrocortisone is unavailable, and never in primary adrenal insufficiency without concurrent fludrocortisone coverage.