Hydrocortisone to Prednisolone Conversion
The standard conversion ratio is 4:1, meaning 20 mg of hydrocortisone equals 5 mg of prednisolone (or 4 mg of hydrocortisone equals 1 mg of prednisolone). This conversion applies to both adult and pediatric dosing for glucocorticoid replacement therapy.
Standard Conversion Ratios
The FDA-approved drug labels provide clear equivalency data 1, 2:
- 20 mg hydrocortisone = 5 mg prednisolone (4:1 ratio)
- For practical dosing: 4 mg hydrocortisone = 1 mg prednisolone
This 4:1 conversion ratio is consistently supported across multiple sources 1, 3 and represents the standard for clinical practice.
Adult Dosing Conversion
For maintenance replacement therapy in adrenal insufficiency:
- Typical hydrocortisone dose: 15-25 mg daily (divided into 2-3 doses)
- Equivalent prednisolone dose: 3.75-6.25 mg daily (typically given once daily in the morning)
Recent evidence suggests that once-daily prednisolone at 2-5 mg is effective for adrenal insufficiency replacement 4, which aligns with the 4:1 conversion from standard hydrocortisone replacement doses of 15-25 mg daily.
Pediatric Dosing Conversion
For children with adrenal insufficiency 5:
- Hydrocortisone: 8 mg/m² body surface area per day (divided into 3-4 doses)
- Prednisolone equivalent: 2 mg/m² body surface area per day
Important pediatric consideration: Guidelines recommend hydrocortisone over prednisolone in children 5 because hydrocortisone's shorter half-life allows easier dose titration and minimizes growth suppression risks. Prednisolone should generally be avoided in pediatric maintenance therapy.
Stress Dosing Conversions
During acute illness or stress 6, 5:
For Adults:
- Hydrocortisone stress dose: 40 mg daily (e.g., 10 mg four times daily)
- Prednisolone equivalent: 10 mg daily (given in 1-2 divided doses)
For Adrenal Crisis:
- Hydrocortisone: 100 mg IV bolus, then 200 mg/24 hours
- Prednisolone alternative: Can be used if hydrocortisone unavailable 5, though hydrocortisone is strongly preferred
For Children in Crisis:
- Hydrocortisone: 50-100 mg/m² bolus, then 50-100 mg/m²/day divided every 6 hours 5
- Prednisolone: May substitute using 4:1 conversion if hydrocortisone unavailable 7
Critical Clinical Caveats
Route-specific warning: The 4:1 conversion ratio applies specifically to oral or intravenous administration. When glucocorticoids are given intramuscularly or intra-articularly, relative potencies may differ significantly 1.
Timing differences: Hydrocortisone has a shorter half-life (8-12 hours) requiring multiple daily doses, while prednisolone has a longer half-life (12-36 hours) allowing once-daily dosing 8, 4. This pharmacokinetic difference means:
- Hydrocortisone better mimics physiologic cortisol rhythm when dosed 2-3 times daily
- Prednisolone provides more sustained coverage but less physiologic variation
Pregnancy consideration: In pregnant women with adrenal insufficiency, use hydrocortisone over prednisolone 5. While both cross the placenta to some degree, hydrocortisone is preferred, and dexamethasone should be avoided entirely as it is not inactivated by placental enzymes.
Bone and metabolic effects: Recent data shows prednisolone may slow bone turnover more than hydrocortisone and is associated with modest weight reduction 4, though clinical significance for long-term bone health requires further study.
Practical Application Algorithm
- Calculate the conversion: Divide hydrocortisone dose by 4 to get prednisolone equivalent
- Adjust timing: Convert from multiple daily hydrocortisone doses to once-daily morning prednisolone
- Monitor clinically: Assess for signs of over-replacement (weight gain, hypertension, hyperglycemia) or under-replacement (fatigue, hypotension, weight loss)
- Special populations:
- Children: Prefer hydrocortisone; avoid prednisolone for maintenance
- Pregnancy: Use hydrocortisone only
- Stress dosing: Maintain 4:1 ratio but increase total glucocorticoid exposure appropriately