Corticosteroid Dose Equivalence and Interchange Between Dexamethasone and Prednisone
When interchanging between dexamethasone and prednisone, the standard conversion ratio is 1 mg of dexamethasone equals 6-7 mg of prednisone, based on their relative potencies.
Relative Potency and Conversion Factors
Dexamethasone is significantly more potent than prednisone due to its molecular structure and pharmacodynamic properties:
- Dexamethasone is approximately 6-7 times more potent than prednisone 1
- Dexamethasone is approximately 25 times more potent than hydrocortisone 1, 2
- Prednisone is approximately 4 times more potent than hydrocortisone 1
Standard Conversion Table:
| Corticosteroid | Equivalent Dose (mg) | Relative Potency |
|---|---|---|
| Dexamethasone | 1 mg | 6-7x |
| Prednisone | 6-7 mg | 1x |
| Hydrocortisone | 25 mg | 0.25x |
Clinical Applications of Conversion
The conversion ratio should be applied in various clinical scenarios:
Anti-inflammatory/Immunosuppressive Use:
- A standard prednisone dose of 60 mg/day would convert to approximately 10 mg/day of dexamethasone 1
- For pediatric dosing, prednisone 1-2 mg/kg/day would convert to dexamethasone 0.15-0.3 mg/kg/day 3
Antiemetic Use in Oncology:
- For chemotherapy-induced nausea and vomiting, 8-12 mg of dexamethasone is equivalent to approximately 48-72 mg of prednisone 1
Acute Asthma Exacerbations:
- 50 mg of prednisone daily for 5 days can be substituted with 16 mg of dexamethasone daily for 2 days with similar efficacy 4
- In pediatric patients, prednisone 1-2 mg/kg daily for 5 days is equivalent to dexamethasone 0.3-0.6 mg/kg daily for 1-5 days 3
Duration Considerations
The biological half-life differs significantly between these medications, affecting dosing frequency:
- Dexamethasone: 36-54 hours (long-acting)
- Prednisone: 12-36 hours (intermediate-acting)
This difference explains why dexamethasone can often be dosed less frequently than prednisone while maintaining efficacy. For example, in acute asthma treatment, a 2-day course of dexamethasone can be as effective as a 5-day course of prednisone 4.
Special Considerations
Pharmacodynamic Differences:
- Dexamethasone causes less sodium retention than prednisone
- Dexamethasone has greater penetration across the blood-brain barrier
- Dexamethasone has minimal mineralocorticoid activity compared to prednisone
Clinical Cautions:
- When converting between these medications, consider the indication, duration of therapy, and patient-specific factors
- Morning dosing of dexamethasone causes less HPA axis suppression than evening dosing 2
- For long-term therapy, tapering is essential when switching between corticosteroids to prevent adrenal insufficiency
- Medications affecting CYP3A4 can alter corticosteroid metabolism, potentially requiring dose adjustments 1, 2
Practical Conversion Examples
- Acute inflammation: Prednisone 40 mg daily ≈ Dexamethasone 6-7 mg daily
- Chemotherapy antiemetic: Dexamethasone 8 mg ≈ Prednisone 48-56 mg
- Immune thrombocytopenia: Prednisone 1-2 mg/kg/day ≈ Dexamethasone 0.6 mg/kg/day for 4 days in pulsed cycles 5
Remember that while these conversion ratios provide a good starting point, clinical response should be monitored when switching between corticosteroids, as individual patient responses may vary.