Hydrocortisone Pharmacokinetics: Time to Peak and Duration of Action
Oral hydrocortisone reaches peak plasma concentration at approximately 1 hour (range 0.3-3 hours) with a duration of action of 6-9 hours, while intravenous hydrocortisone achieves peak levels within 10 minutes and requires dosing every 4-6 hours to maintain therapeutic levels.
Oral Administration Pharmacokinetics
Time to Peak:
- Peak plasma cortisol concentrations occur at 1-1.2 hours after oral administration 1, 2, 3
- Range: 0.3-3.3 hours depending on individual variation 2
- Absorption is rapid with bioavailability of 94-96% 2, 3
Duration of Action:
- Cortisol becomes undetectable at 7-9 hours after morning dose 2
- Evening doses may persist slightly longer (up to 9 hours, range 5-12 hours) due to decreased clearance 2
- Elimination half-life: 1.2-1.7 hours (increases with higher doses) 3, 4
Clinical Implications:
- The 20 mg oral dose produces supraphysiological peak concentrations (729.5 nmol/L median) 1
- This explains why twice or thrice daily dosing is standard practice
- Evening bioavailability may be higher (128%) due to reduced clearance 2
Intravenous Administration Pharmacokinetics
Time to Peak:
- Peak plasma concentration occurs at 10 minutes (range 10-20 minutes) after IV bolus 2, 5
- Immediate effects are evident within 1 hour of IV administration 6
- Hydrocortisone succinate converts rapidly to hydrocortisone with a half-life of 5.4 minutes 5
Duration of Action:
- Excretion is nearly complete within 12 hours 6
- Therapeutic levels require dosing every 4-6 hours to maintain constant blood levels 6
- Cortisol becomes undetectable approximately 6 hours after IV bolus 2
- Elimination half-life: 1.7 hours 3
Practical Dosing Guidance Based on Pharmacokinetics
For Stress Dosing (Perioperative/Critical Illness):
The 2020 UK guidelines recommend 7:
- 100 mg IV bolus followed by continuous infusion of 200 mg/24 hours
- Alternative: 50 mg every 6 hours IM or IV
- This maintains physiological stress levels (equivalent to ~100 mg cortisol/day production during major surgery) 7
Key Pharmacokinetic Principle: Given the 4-6 hour duration of action, continuous infusion is superior to intermittent boluses for maintaining stable cortisol levels during critical illness 6. The every-6-hour dosing represents the minimum acceptable frequency based on the drug's elimination kinetics.
For Routine Replacement:
- Standard 20 mg oral dose is supraphysiological at peak 1
- Consider divided dosing (e.g., 10 mg morning, 5 mg afternoon, 5 mg evening) to better mimic physiological cortisol rhythm
- Avoid single daily dosing given the 6-9 hour duration of action
Common Pitfalls
- Underdosing in acute stress: The 50 mg IV every 6 hours provides only 200 mg/day total, which may be inadequate for severe stress requiring 300-400 mg/day
- Excessive peak levels with oral dosing: The 1-hour peak can cause supraphysiological levels; this is unavoidable with current formulations
- Assuming IM equals IV: While bioavailability is similar, IM absorption is slower and less predictable in shock states
- Premature discontinuation: Given the 6-hour duration, stopping hydrocortisone abruptly can lead to relative adrenal insufficiency; taper over 24-48 hours when clinically stable 7