Is Regular Insulin Short-Acting?
Yes, regular insulin is definitively classified as a short-acting insulin. 1, 2
Classification and Pharmacokinetics
Regular insulin (also called regular human insulin) is categorized as a short-acting insulin in the standard insulin classification system, which distinguishes it from rapid-acting analogs, intermediate-acting, and long-acting insulins. 1
Onset and Duration of Action
Regular insulin has the following pharmacokinetic profile when administered subcutaneously: 2
- Onset of action: Approximately 30 minutes (range: 10-75 minutes) after subcutaneous injection
- Peak effect: Approximately 3 hours (range: 20 minutes to 7 hours)
- Duration of action: Approximately 8 hours (range: 3-14 hours)
For intravenous administration, regular insulin acts even faster, with onset at approximately 10-15 minutes and termination at a median of 4 hours (range: 2-6 hours). 2
Comparison to Other Insulin Types
Regular insulin is distinct from rapid-acting insulin analogs (such as insulin lispro, insulin aspart, and insulin glulisine), which have a quicker onset and peak with shorter duration of action than regular human insulin. 1 The rapid-acting analogs begin exerting effects within 15 minutes of administration with peak levels at 30-90 minutes and duration less than 5 hours. 3
Regular insulin is also distinct from intermediate-acting insulins (such as NPH and lente) and long-acting insulins (such as ultralente and insulin glargine). 1
Clinical Implications
Visual Inspection
Regular insulin should appear clear and colorless on visual examination, similar to rapid-acting insulins and insulin glargine, while all other insulin types should be uniformly cloudy. 1
Mixing Considerations
When mixing regular insulin with intermediate-acting insulins: 1
- Regular insulin should be drawn into the syringe first when mixing with NPH
- Mixing of regular insulin with lente insulins is not recommended except for patients already well-controlled on such mixtures, as zinc in lente insulins can bind with regular insulin and delay its onset of action
- NPH and regular insulin formulations when mixed may be used immediately or stored for future use
Timing of Administration
Regular insulin should be administered approximately 30 minutes before meals when used subcutaneously, which differs from rapid-acting analogs that can be given within 15 minutes of eating. 2
Historical Context
Regular insulin was the short-acting insulin used in landmark trials including the Diabetes Control and Complications Trial (DCCT), where it was combined with intermediate-acting NPH insulin to demonstrate the benefits of intensive glycemic control. 1
Human insulin analogs were subsequently developed to overcome the limitations of regular insulin, including its delayed onset of action, late peak, and prolonged tail that can lead to postprandial hyperglycemia and late hypoglycemia. 4, 5