How do I convert insulin aspart (novolog) units to insulin regular (human insulin) units?

Converting Insulin Aspart Units to Regular Insulin Units

When converting from insulin aspart (NovoLog) to regular human insulin (Humulin R), the units can be converted on a one-to-one basis, but timing of administration must be adjusted due to their different pharmacokinetic profiles.

Key Conversion Principles

• Insulin aspart and regular insulin can be converted on a unit-per-unit basis (1:1 ratio), but regular insulin must be administered 30 minutes before meals rather than immediately before meals as with insulin aspart 1, 2
• Regular insulin has a slower onset of action (30-60 minutes vs. 10-20 minutes) and longer duration of action (6-8 hours vs. 3-5 hours) compared to insulin aspart 1, 3
• When switching from insulin aspart to regular insulin, maintain the same total daily dose initially, but adjust the timing of administration to 30 minutes before meals 2, 3

Dosing Considerations

• For basal-bolus regimens, maintain the same basal insulin dose (NPH or long-acting analog) when switching between prandial insulins 4
• For patients previously on insulin aspart who are switching to regular insulin:
  • Start with the same number of units as the previous insulin aspart dose 4
  • Administer regular insulin 30 minutes before meals instead of immediately before meals 1, 5
  • Monitor blood glucose closely for 3-5 days after switching to determine if dose adjustments are needed 6

Monitoring After Conversion

• Check blood glucose levels at least 4 times daily during the adjustment period 6
• Pay special attention to:
  • Fasting morning glucose levels
  • 2-hour postprandial values
  • Signs of hypoglycemia, particularly in the late postprandial period (4-6 hours after meals) 2
• Evaluate glucose patterns over 3-5 days before making additional adjustments 6

Potential Pitfalls

• Regular insulin requires more advance planning as it must be administered 30 minutes before meals, unlike insulin aspart which can be given immediately before eating 1, 3
• Failure to adjust administration timing when switching from insulin aspart to regular insulin may result in postprandial hyperglycemia 2, 5
• Regular insulin has a higher risk of late postprandial hypoglycemia (4-6 hours after meals) compared to insulin aspart due to its longer duration of action 2
• Patients may experience more glycemic variability with regular insulin compared to insulin aspart 5, 7

Special Situations

• For patients on continuous subcutaneous insulin infusion (insulin pump), switching from insulin aspart to regular insulin is generally not recommended due to the pharmacokinetic advantages of rapid-acting analogs in pump therapy 3
• For patients using premixed insulins, conversion should be done carefully as the pharmacokinetic profiles differ significantly between premixed aspart formulations and regular/NPH premixes 3