What is the effect of 1 unit of Novorapid (insulin aspart) on glucose levels in a patient with insulin-dependent diabetes?

Glucose Reduction Effect of 1 Unit NovoRapid

One unit of NovoRapid (insulin aspart) typically reduces blood glucose by approximately 2-3 mmol/L (30-50 mg/dL) in adults with diabetes, though individual response varies significantly based on insulin sensitivity, body weight, and insulin resistance. 1, 2

Understanding the Insulin Sensitivity Factor

The glucose-lowering effect of rapid-acting insulin is highly individualized and calculated using the insulin sensitivity factor (ISF), also called the correction factor. 1, 2

Standard Calculation Methods

• The "1500 rule" is commonly used: ISF = 1500 ÷ Total Daily Dose (TDD) of insulin 1
• The "1800 rule" provides an alternative calculation for some patients 2
• For example, if a patient uses 50 units of insulin daily, their ISF would be 1500 ÷ 50 = 30 mg/dL per unit (approximately 1.7 mmol/L per unit) 1

Practical Clinical Application

In hospital settings, simplified correction protocols suggest that 2 units of rapid-acting insulin are given for glucose elevations of approximately 5.5-11 mmol/L above target, implying roughly 1.4-2.8 mmol/L reduction per unit. 2

For hospitalized patients with premeal glucose >13.9 mmol/L (250 mg/dL), guidelines recommend 2 units of rapid-acting insulin, and for glucose >19.4 mmol/L (350 mg/dL), 4 units are recommended—this implies an expected reduction of approximately 2.8 mmol/L per unit. 2

Factors That Significantly Affect Individual Response

Body Weight and Insulin Resistance

• Heavier patients and those with higher insulin resistance require more insulin to achieve the same glucose reduction 2
• Insulin-sensitive individuals may experience reductions closer to 2-3 mmol/L per unit, while insulin-resistant patients may see only 1-2 mmol/L per unit 2

Time of Day

• Morning hours often require more insulin per gram of carbohydrate due to counter-regulatory hormones like cortisol and growth hormone 2
• This dawn phenomenon means 1 unit may lower glucose less effectively in the morning compared to evening 2

Physical Activity

• Exercise increases insulin sensitivity, meaning 1 unit will lower glucose more effectively during or after physical activity 2
• This effect can persist for hours after exercise completion 3

Context-Dependent Glucose Reduction

Correction Doses (Without Food)

For correction doses given without concurrent food intake, the glucose reduction per unit is more predictable and typically falls in the 2-3 mmol/L range for insulin-sensitive individuals. 2

Mealtime Dosing

When NovoRapid is given with meals, the primary purpose is to blunt postprandial glucose excursions rather than simply lower glucose by a fixed amount. 4, 5

The insulin-to-carbohydrate ratio (ICR) determines how many grams of carbohydrate are covered by 1 unit, typically starting at 1 unit per 10-15 grams of carbohydrate. 1

Practical Dosing Approach

Start conservatively with the assumption that 1 unit will reduce glucose by approximately 2.0 mmol/L (36 mg/dL) in insulin-sensitive individuals, and adjust based on observed response over 3-4 hours. 2

Critical Safety Consideration

Stacking insulin doses within 3-4 hours increases hypoglycemia risk significantly, as NovoRapid has a duration of action of 3-5 hours. 2, 6

Common Pitfalls to Avoid

• Never assume a fixed glucose reduction applies to all patients—always calculate individualized ISF based on total daily insulin dose 1, 2
• Avoid giving correction doses more frequently than every 3-4 hours to prevent insulin stacking and severe hypoglycemia 2
• Do not use the same correction factor throughout the day—morning insulin resistance may require different calculations than evening doses 2
• Recalculate ISF periodically during illness, changes in physical activity patterns, or significant weight changes 2

Monitoring Requirements

• Check blood glucose 2 hours after NovoRapid administration to assess adequacy of the dose and individual response 1
• For hospitalized patients, maintain a target glucose range of 7.8-10.0 mmol/L (140-180 mg/dL) 2
• For outpatients with diabetes, fasting goals of 5.0-8.3 mmol/L (90-150 mg/dL) are appropriate for stable patients 2