What is the equivalent dose of prednisone when converting from dexamethasone?

Dexamethasone to Prednisone Dose Conversion

The standard conversion ratio is 1 mg dexamethasone equals 5 mg prednisone (1:5 ratio), meaning 4 mg dexamethasone converts to 20 mg prednisone. 1, 2

Standard Conversion Ratios

• Dexamethasone is approximately 5 times more potent than prednisone on a milligram-per-milligram basis 1
• The most commonly cited conversion is 1 mg dexamethasone = 5 mg prednisone 1
• Alternative sources describe this as a 1:2.5 ratio when converting from dexamethasone to prednisone (8 mg dexamethasone = 20 mg prednisone), which is mathematically equivalent 2

Common Conversion Examples

• Dexamethasone 1 mg = Prednisone 5 mg 1
• Dexamethasone 4 mg = Prednisone 20 mg 1, 2
• Dexamethasone 10 mg = Prednisone 60 mg 1
• Dexamethasone 6 mg IV = Prednisolone 30 mg oral (perioperative context) 1

Clinical Context Considerations

Oncology Applications

• In multiple myeloma regimens, dexamethasone 40 mg is used on specific days as part of combination therapy 3
• When converting prednisone 5 mg twice daily to dexamethasone, use approximately 4 mg dexamethasone once daily 2
• For abiraterone therapy in prostate cancer, prednisone 10 mg daily converts to dexamethasone 0.5-1 mg daily (lower ratio used to minimize mineralocorticoid effects) 2

Hematologic Conditions

• For immune thrombocytopenia, dexamethasone 40 mg daily for 4 days can substitute for prednisone 0.5-2 mg/kg/day, though prednisone is preferred in children due to better tolerability 2
• Research demonstrates that dexamethasone 0.6 mg/kg/day for 4 days per cycle (pulsed dosing) produces superior long-term remission rates compared to daily prednisone 1-2 mg/kg/day in immune thrombocytopenia 4

Acute Lymphoblastic Leukemia

• At prednisone-to-dexamethasone ratios less than 7:1, dexamethasone (6-18 mg/m² per day) demonstrates superior efficacy compared to prednisone (40-120 mg/m² per day) 5
• At ratios greater than 7:1, the two drugs show equivalent efficacy 5
• Dexamethasone provides better CNS penetration and improved control of CNS leukemia 3, 5

Acute Asthma Exacerbations

• Dexamethasone 0.3-0.6 mg/kg daily for 1-5 days is equivalent to prednisone 1-2 mg/kg daily for 5 days in pediatric patients 6
• A single 12 mg dose of dexamethasone nearly matches the efficacy of prednisone 60 mg daily for 5 days in adults (relapse rates 12.1% vs 9.8%) 7

Important Pharmacologic Differences

• Dexamethasone has minimal mineralocorticoid activity compared to prednisone, making direct conversions potentially misleading when mineralocorticoid effects are clinically relevant 2
• Dexamethasone has a longer half-life (36-72 hours) compared to prednisone (12-36 hours), allowing for less frequent dosing 5
• Single daily dosing is recommended for dexamethasone rather than divided doses 1

Toxicity Profile Considerations

Dexamethasone-Specific Risks

• Higher risk of osteonecrosis and bone fractures, particularly at doses ≥10 mg/m² per day 3, 5
• More frequent insomnia and mood/behavior disturbances compared to prednisone 5, 4
• Increased infection risk, especially with prolonged high-dose therapy 3, 5

Prednisone-Specific Risks

• More frequent infectious complications in some studies compared to pulsed dexamethasone 4
• Higher rates of vomiting compared to dexamethasone in acute asthma (emergency department: RR 0.29 for dexamethasone; at home: RR 0.32) 8

Critical Caveats

• The conversion ratio varies by clinical context and should not be applied universally across all conditions 2
• Individual patient cytotoxic responses differ substantially, particularly in ALL, where the dose ratio producing equivalent effects varies between patients 5
• Selection of corticosteroid type and dose should be based on relapse risk, treatment phase, and concurrent chemotherapy 5
• Patients taking prednisone ≥20 mg daily (or dexamethasone ≥4 mg daily equivalent) may have blunted vaccine responses 1