Novolog (Insulin Aspart) is Rapid-Acting and Uses the 300 Rule for Breakfast and 400 Rule for Lunch/Dinner
For patients taking Novolog (insulin aspart), which is a rapid-acting insulin, use the 300 rule for breakfast and the 400 rule for lunch and dinner when calculating insulin-to-carbohydrate ratios. 1
Characteristics of Novolog (Insulin Aspart)
- Novolog is classified as a rapid-acting insulin with onset within 5 minutes, peak action at 1-2 hours, and duration of 3-4 hours 2
- It is designed to control postprandial blood glucose more effectively than regular insulin, allowing for administration immediately before meals rather than 30 minutes prior 2, 3
- Rapid-acting insulins like Novolog provide better glycemic control but can cause a more rapid onset of hypoglycemia if dosed incorrectly 2
Insulin-to-Carbohydrate Ratio Calculation Rules
- For patients taking Novolog at breakfast: Use the 300 rule (CIR = 300 ÷ Total Daily Insulin Dose) 1
- For patients taking Novolog at lunch and dinner: Use the 400 rule (CIR = 400 ÷ Total Daily Insulin Dose) 1
- This diurnal variance in insulin sensitivity is significant, with breakfast typically requiring more insulin per gram of carbohydrate than other meals 1, 4
Clinical Evidence Supporting Different Rules
- Research demonstrates that the previously established calculation of CIR = 500 ÷ TDD underestimates insulin requirements, particularly at breakfast 1
- A study of patients with type 1 diabetes found that the median breakfast rule was 211, while for other meals it was 434, supporting the use of different calculations throughout the day 5
- Insulin requirements are consistently greater in the morning than in the evening, even when meal size is constant, due to diurnal variations in insulin sensitivity 4
Practical Application
- Calculate the patient's total daily insulin dose (TDD) first 6
- For breakfast bolus: Divide 300 by TDD to determine how many grams of carbohydrate are covered by 1 unit of insulin 1
- For lunch and dinner bolus: Divide 400 by TDD to determine how many grams of carbohydrate are covered by 1 unit of insulin 1
- Example: If TDD is 40 units, breakfast ratio would be 300 ÷ 40 = 7.5 (1 unit covers 7.5g carbs), while lunch/dinner would be 400 ÷ 40 = 10 (1 unit covers 10g carbs)
Important Considerations
- Basal insulin typically accounts for approximately 50% of the total daily insulin requirement, though this may vary particularly in children 2
- When using insulin pumps, temporary basal rates can be programmed to account for variations in daily activities and insulin sensitivity 2
- For patients on multiple daily injections, consistent carbohydrate intake day-to-day helps maintain glycemic control when using fixed insulin doses 2
Potential Pitfalls
- Using a single rule throughout the day may lead to under-dosing at breakfast and potential hyperglycemia 1, 5
- Failing to account for the dawn phenomenon (increased morning blood glucose due to counter-regulatory hormones) can result in inadequate breakfast insulin dosing 2
- Very large meals with high fat and carbohydrate content may require significantly more insulin than calculated by standard ratios 4
By using the appropriate rule based on the time of day (300 rule for breakfast, 400 rule for lunch/dinner), patients taking Novolog can achieve more precise insulin dosing and better glycemic control.