Dexamethasone to Prednisolone Conversion
1 mg of dexamethasone is equivalent to approximately 5 mg of prednisolone, based on the standard 5:1 conversion ratio used in clinical practice. 1, 2
Standard Conversion Ratio
The established conversion ratio between these corticosteroids is 5:1 (prednisolone:dexamethasone), meaning:
- Prednisolone 5 mg = Dexamethasone 1 mg 1, 2
- Prednisolone 20 mg = Dexamethasone 4 mg 1, 2, 3
- Prednisolone 60 mg = Dexamethasone 10 mg 1, 2
This ratio is supported by FDA labeling information, which confirms that 15 mg prednisolone base is equivalent to 2.25 mg dexamethasone, maintaining the approximately 5:1 ratio. 3
Pharmacologic Basis for This Conversion
Dexamethasone is approximately 5 times more potent than prednisolone in terms of glucocorticoid activity. 2 The underlying potency relationships demonstrate that:
- Dexamethasone is 25 times more potent than hydrocortisone 1, 2
- Prednisolone is 5 times more potent than hydrocortisone 1, 2
- Therefore, dexamethasone is 5 times more potent than prednisolone 2
Research studies using mechanistic models for cell trafficking and cortisol dynamics have validated that current corticosteroid dose equivalency tables reflect reasonable dose equivalency relationships. 4
Critical Clinical Considerations When Converting
Dosing Schedule Differences
Dexamethasone should be administered as a single daily dose rather than divided doses, unlike prednisolone which may be given in divided doses. 1, 2 This is due to dexamethasone's longer biological half-life (36-72 hours) compared to prednisolone (12-36 hours). 5, 6
Mineralocorticoid Activity
Dexamethasone has no mineralocorticoid activity, making it inadequate for stress coverage in patients with primary adrenal insufficiency who require both glucocorticoid and mineralocorticoid replacement. 2 Prednisolone retains some mineralocorticoid activity, though less than hydrocortisone.
Potency Variations by Context
The relative potency of dexamethasone compared to prednisolone may be even higher than the 5:1 ratio suggests due to its much longer biological half-life. 7 Studies in neonates suggest that low-dose dexamethasone (0.1-0.15 mg/kg/day) may be equivalent to 3-6 mg/kg/day of hydrocortisone, but because of the longer half-life, it could have much higher relative potency in practice. 7
Common Pitfalls to Avoid
- Do not use the same dose when switching between these medications—the 5-fold difference in potency is substantial and errors can lead to either under-treatment or significant adverse effects 1, 2
- Account for route of administration: The conversion ratios apply to oral or intravenous administration; when injected intramuscularly or into joint spaces, relative properties may be greatly altered 3
- Consider drug interactions: Medications that induce hepatic enzymes (like rifampicin) can accelerate metabolism of both drugs, with dexamethasone metabolism being particularly affected 8