Dexamethasone to Hydrocortisone Equivalency
10 mg of hydrocortisone is equivalent to approximately 0.1 mg of dexamethasone, meaning dexamethasone is roughly 100 times more potent than hydrocortisone. 1
Standard Dose Conversion
The established equivalency ratio is:
- 10 mg hydrocortisone = 0.1 mg dexamethasone 1
- Alternatively stated: 8 mg dexamethasone = 200 mg hydrocortisone 1, 2
This means a single 8 mg dose of dexamethasone provides equivalent glucocorticoid coverage to 200 mg of hydrocortisone for approximately 24 hours due to dexamethasone's significantly longer half-life 1, 2.
Critical Pharmacologic Differences Beyond Potency
Mineralocorticoid Activity
Dexamethasone has zero mineralocorticoid activity, while hydrocortisone possesses both glucocorticoid and mineralocorticoid effects. 1, 2 This distinction is clinically crucial:
- In primary adrenal insufficiency, dexamethasone alone is inadequate for stress coverage because patients require mineralocorticoid replacement that only hydrocortisone can provide 1, 2
- Hydrocortisone is structurally identical to cortisol and binds both mineralocorticoid and glucocorticoid receptors, whereas dexamethasone binds only glucocorticoid receptors 2
Duration of Action
- Hydrocortisone has a plasma elimination half-life of approximately 90 minutes, requiring administration every 6-8 hours or via continuous IV infusion 1, 2
- Dexamethasone is long-acting, providing coverage for 24-48 hours with a single dose 2
Clinical Application Algorithm
Step 1: Identify the Clinical Indication
- For perioperative stress coverage in secondary adrenal insufficiency or chronic glucocorticoid users: Either agent is appropriate, but select based on pharmacokinetics 2
- For primary adrenal insufficiency: Hydrocortisone is mandatory due to mineralocorticoid requirements; dexamethasone alone is contraindicated 1, 2
Step 2: Select Agent Based on Practical Considerations
- Choose dexamethasone (8 mg single dose) when long-acting coverage is desired and mineralocorticoid activity is not needed 2
- Choose hydrocortisone (50 mg IV every 6 hours or continuous infusion) when mineralocorticoid activity is required or shorter-acting control is preferred 1, 2
Step 3: Avoid Combining Both Agents
Do not routinely combine dexamethasone and hydrocortisone, as they work through identical glucocorticoid receptor pathways and combining them simply increases total glucocorticoid burden without additional therapeutic benefit 2. The only exception is primary adrenal insufficiency where hydrocortisone provides necessary mineralocorticoid replacement alongside dexamethasone's glucocorticoid effect 2.
Common Pitfalls to Avoid
- Never use dexamethasone as sole therapy in primary adrenal insufficiency without adding mineralocorticoid replacement (fludrocortisone or hydrocortisone) 1, 2
- Do not reflexively add hydrocortisone to dexamethasone in patients with secondary adrenal insufficiency or those on chronic glucocorticoid therapy, as this causes excessive glucocorticoid exposure 2
- Remember that 8 mg dexamethasone for postoperative nausea/vomiting actually provides full stress-dose steroid coverage (equivalent to 200 mg hydrocortisone) for 24 hours 1
- In patients taking CYP3A4 inducers or obese patients, hydrocortisone doses may need to be higher, and continuous IV infusion is preferred over intermittent dosing 1
Evidence Quality Note
The 100:1 potency ratio (0.1 mg dexamethasone = 10 mg hydrocortisone) is consistently cited across multiple high-quality guidelines including the Association of Anaesthetists/Royal College of Physicians/Society for Endocrinology UK guidelines 1 and American Society of Anesthesiologists recommendations 2, making this equivalency the gold standard for clinical practice.