Duration of Action of Actrapid (Regular Insulin)
Actrapid (regular insulin) has an onset of action at 15 minutes, peaks at 3-4 hours, and has a total duration of action of 6-8 hours in the body. 1
Pharmacokinetic Profile
The complete time-action profile of Actrapid (regular insulin injection) is as follows:
- Onset of action: 15 minutes after subcutaneous injection 1
- Peak effect: 3-4 hours after administration 1
- Duration of action: 6-8 hours total 1
Clinical Implications
Timing Considerations
The relatively slow onset and extended duration of Actrapid means it should ideally be administered 15-30 minutes before meals to achieve optimal postprandial glucose control, rather than immediately before eating. 2 Research in diabetic children demonstrated that injecting regular insulin 30 minutes before breakfast resulted in consistently lower postprandial blood glucose concentrations compared to injection 5 minutes before the meal, with the greatest difference (3.7 mmol/L) occurring 150 minutes after breakfast. 2
Comparison to Rapid-Acting Analogues
Actrapid has significantly slower pharmacokinetics compared to modern rapid-acting insulin analogues (such as lispro and aspart), which have:
This means rapid-acting analogues provide better postprandial glucose control and can be administered immediately before meals, whereas Actrapid requires advance planning. 3, 4
Important Caveats
Mixing with Other Insulins
When Actrapid is mixed with intermediate-acting insulins (such as NPH/Monotard), its absorption rate may be slightly delayed. 5 Studies show that the incremental area of free insulin up to 90 minutes after administration was lower when regular insulin was mixed with intermediate-acting insulin (21 ± 3 vs. 32 ± 5 microU × ml⁻¹ × min⁻¹), though this difference may not be clinically significant in practice. 5
Hypoglycemia Risk
The extended duration of action (6-8 hours) creates a higher risk of late postprandial hypoglycemia compared to rapid-acting analogues, particularly if meals are delayed or physical activity increases during this period. 1 Patients must be counseled to eat at consistent intervals when using regular insulin to avoid hypoglycemia during the extended tail of insulin action. 1