Corticosteroid equivalence calculator

Corticosteroid equivalence converts between agents on glucocorticoid potency, where 5 mg prednisolone is roughly 20 mg hydrocortisone and 0.75 mg dexamethasone. Potency alone is not the whole answer, because mineralocorticoid activity and duration differ independently of it.

When to use the steroid equivalence calculator

Use to compare anti-inflammatory potency between corticosteroids. These ratios are standard teaching and appear constantly in examinations.

The steroid equivalence formula

Equivalent dose = (dose ÷ equivalence value of the starting steroid) × equivalence value of the target steroid. The reference set is hydrocortisone 20 mg, prednisone 5 mg, methylprednisolone 4 mg, dexamethasone 0.75 mg.

Worked example

Prednisone 40 mg converted to dexamethasone. (40 ÷ 5) × 0.75 = 8 × 0.75 = 6 mg of dexamethasone.

The mistake that costs marks

Equivalence covers glucocorticoid effect only, and the other two properties are what questions actually turn on. Mineralocorticoid activity falls as you move up the table, so hydrocortisone causes sodium and water retention while dexamethasone has essentially none. Duration rises in the same direction: hydrocortisone acts for 8 to 12 hours, prednisone for 12 to 36, and dexamethasone for 36 to 72. A dose-equivalent swap is therefore not a clinically equivalent swap.

Study aid, not a clinical tool

This calculator exists so you can learn the method and check your working for an examination. It is not medical advice and not clinical decision support, and it must not be used to make a decision about a real patient. Verify any result against your local formulary, the product literature and a qualified pharmacist. Our medical disclaimer sets out the full position.

Calculators you will usually need alongside this

Most questions that reach for one of these reach for another a step later, so these are the three that most often pair with it.

• mg/kg dose calculator — Weight-based dose
• Half-life and steady state calculator — Half-life
• Creatinine clearance calculator (Cockcroft-Gault) — Creatinine clearance

Keep going

Calculations are only half of what examinations test. The other half is knowing why a drug does what it does, which is what decides whether a number you calculated is even the right number to be calculating. Start with CYP450 inducers and inhibitors. The drug class pages cover the mechanism behind the number, or browse the rest of the free calculators and try the practice questions.