Insulin Onset of Action
Rapid-acting insulin analogs (lispro, aspart) begin working within 5-15 minutes of subcutaneous injection, while short-acting regular insulin takes 15 minutes to onset. 1, 2, 3
Rapid-Acting Insulin Analogs (Lispro, Aspart)
The onset of action for rapid-acting insulin analogs is 5 minutes after subcutaneous administration. 1, 2
- Peak effect occurs at 1-2 hours post-injection 1, 2
- Total duration of action is 3-4 hours 1, 2
- The FDA label for insulin aspart confirms maximum glucose-lowering effect occurs between 1-3 hours, with duration of 3-5 hours 4
- Insulin lispro begins exerting effects within 15 minutes, with peak levels at 30-90 minutes and duration less than 5 hours 3
Clinical Implications of Rapid Onset
Rapid-acting analogs can be administered immediately before meals (0-15 minutes prior) or even after meals in young children with unpredictable eating. 2, 5
- The rapid onset means hypoglycemia can develop quickly, giving patients less warning time to recognize symptoms 2
- Patients require thorough education on hypoglycemia recognition and treatment due to the fast action profile 2
Short-Acting Regular Insulin (Actrapid)
Regular insulin has an onset of action at 15 minutes after subcutaneous injection. 1
- Peak effect occurs at 3-4 hours post-administration 1
- Total duration of action is 6-8 hours 1
- The median time to maximum concentration is 80-120 minutes for regular human insulin versus 40-50 minutes for rapid-acting analogs 4
Clinical Implications of Delayed Onset
The extended duration of regular insulin creates higher risk of late postprandial hypoglycemia, particularly if meals are delayed or physical activity increases during the 6-8 hour action period. 1
- Regular insulin must be administered 30-45 minutes before meals, unlike rapid-acting analogs 6
- This longer pre-meal timing requirement reduces flexibility in dosing and mealtime scheduling 7
Key Pharmacokinetic Differences
Rapid-acting analogs achieve earlier and higher insulin peaks with more rapid return to baseline compared to regular insulin. 5
- The faster absorption of rapid-acting analogs is due to more rapid dissociation into monomers after injection, as the amino acid modifications prevent hexamer formation 5
- Injection site affects timing: absorption from the abdomen is 1 hour faster than from the thigh for rapid-acting insulin, compared to 2-3 hours difference for regular insulin 5
- When rapid-acting insulin is mixed with NPH, lente, or ultralente, it should be injected within 15 minutes before a meal 8