Insulin Lispro Classification
Insulin lispro is a rapid-acting (short-acting) insulin analog with a duration of action of 3 to 4 hours. 1, 2
Pharmacokinetic Profile
Insulin lispro has three defining characteristics that classify it as rapid-acting:
- Onset of action: 5 minutes 1, 2
- Peak effect: 1 to 2 hours 1, 2
- Duration of action: 3 to 4 hours 1, 2, 3
This pharmacokinetic profile is fundamentally different from other insulin categories. Regular human insulin, by comparison, has a 15-minute onset, peaks at 3-4 hours, and lasts 6-8 hours, making it intermediate in speed compared to rapid-acting analogs. 1 True intermediate-acting insulins like NPH have a 1-hour onset, peak at 6-8 hours, and last approximately 12 hours. 1
Clinical Significance of the Rapid-Acting Classification
The American Diabetes Association confirms that rapid-acting analogs like lispro have a quicker onset and peak with shorter duration of action than regular human insulin, making them effective for controlling postprandial glucose excursions while minimizing delayed hypoglycemia risk. 1
Key clinical implication: The short 3-4 hour action period means that without adequate basal insulin coverage, blood glucose levels become unstable during gaps between rapid-acting insulin doses. 2 This is why lispro is designed specifically as prandial (mealtime) insulin and must be combined with a long-acting basal insulin (such as glargine or degludec) for comprehensive diabetes management. 1
Practical Dosing Considerations
- Lispro should be administered within 15 minutes before meals, offering significantly more flexibility than the 30-40 minute pre-meal timing required for regular insulin. 2, 4
- In very young children with erratic eating patterns, lispro can be administered after meals to more accurately match actual food intake. 1
- The rapid onset allows for greater flexibility in dosing and mealtime scheduling compared to older insulin formulations. 5
Common Pitfall to Avoid
Do not confuse "short-acting" with "short duration" in older terminology. In contemporary diabetes management, "rapid-acting" is the preferred and accurate term for insulin lispro. 1 The term "short-acting" historically referred to regular human insulin, which is actually slower than lispro. The classification system now uses: rapid-acting analogs (lispro, aspart), regular/short-acting insulin, intermediate-acting (NPH), and long-acting analogs (glargine, degludec). 1