How many millimoles per liter does one unit of NovoRapid (insulin aspart) lower blood glucose?

How Much Does 1 Unit of NovoRapid Lower Blood Glucose?

One unit of NovoRapid (insulin aspart) typically lowers blood glucose by approximately 1.7-2.8 mmol/L (30-50 mg/dL) in most adults, though this varies significantly based on individual insulin sensitivity.

Understanding the Insulin Sensitivity Factor (ISF)

The glucose-lowering effect of rapid-acting insulin like NovoRapid is calculated using the Insulin Sensitivity Factor (ISF), also called the correction factor. The most commonly used formula is 1:

• 1800 ÷ Total Daily Dose (TDD) of insulin = mg/dL drop per unit
• 100 ÷ Total Daily Dose (TDD) of insulin = mmol/L drop per unit

Practical Examples:

• If someone uses 50 units/day total: 100 ÷ 50 = 2.0 mmol/L drop per unit (or 1800 ÷ 50 = 36 mg/dL)
• If someone uses 30 units/day total: 100 ÷ 30 = 3.3 mmol/L drop per unit (or 1800 ÷ 30 = 60 mg/dL)
• If someone uses 80 units/day total: 100 ÷ 80 = 1.25 mmol/L drop per unit (or 1800 ÷ 80 = 22.5 mg/dL)

Important Caveats

This formula is only a starting point and must be adjusted empirically for each person 1. The actual glucose-lowering effect depends on:

• Insulin resistance level: More resistant individuals need higher doses for the same effect
• Body weight: Heavier individuals typically require more insulin
• Renal function: Impaired kidney function increases insulin sensitivity
• Age: Elderly patients (≥70 years) are more insulin-sensitive
• Nutritional status: Malnourished or low BMI patients are more sensitive
• Timing of meals: Insulin action varies with food intake

Clinical Application in Different Settings

Hospital Correction Doses

The guidelines provide standardized correction scales for hospitalized patients 2:

For insulin-sensitive patients (elderly, renal impairment, not eating):

• Glucose 7.8-10.0 mmol/L (141-180 mg/dL): Give 2 units
• Glucose 10.1-12.2 mmol/L (181-220 mg/dL): Give 4 units

For usual patients:

• Glucose 7.8-10.0 mmol/L: Give 4 units
• Glucose 10.1-12.2 mmol/L: Give 6 units

For insulin-resistant patients (on steroids, requiring >80 units/day):

• Glucose 7.8-10.0 mmol/L: Give 6 units
• Glucose 10.1-12.2 mmol/L: Give 8 units

Simplified Sliding Scale for Older Adults

For older adults with simplified regimens 3:

• Premeal glucose >13.9 mmol/L (>250 mg/dL): Give 2 units of rapid-acting insulin
• Premeal glucose >19.4 mmol/L (>350 mg/dL): Give 4 units of rapid-acting insulin

This suggests approximately 1 unit per 3.3 mmol/L (60 mg/dL) in this population.

Pharmacokinetic Considerations

NovoRapid has distinct absorption characteristics that affect its glucose-lowering profile 4:

• Peak effect (Tmax): 52-60 minutes after injection
• Peak insulin concentration: Approximately 500 pmol/L with 0.2 U/kg dose
• Duration of action: 4-6 hours 1
• Onset: Significantly faster than regular insulin (earlier glucose-lowering by 40-80 minutes)

The injection site matters less for NovoRapid than regular insulin—abdomen, deltoid, and thigh all produce similar peak effects, though abdominal injection has a slightly shorter duration 4.

Key Clinical Pitfalls to Avoid

1. Don't stack insulin: Wait at least 4 hours between correction doses to avoid "insulin on board" causing hypoglycemia 1

2. Adjust for insulin resistance: The 1800 rule assumes average sensitivity. Patients on high-dose insulin (>80 units/day) or steroids need less glucose drop per unit 2

3. Lower starting estimates for high-risk patients: Use more conservative correction factors (assume less glucose drop per unit) in:

   • Elderly patients (≥70 years)
   • Renal impairment (GFR <60 mL/min)
   • Patients not eating regularly
   • Starting dose: 0.2-0.3 U/kg/day 2, 1

4. The formula is empirical: Real-world insulin sensitivity varies by 2-3 fold between individuals. Always titrate based on actual glucose response rather than relying solely on calculations 1.

Bottom Line for Practice

While the 1800 rule (or 100 rule in mmol/L) provides a reasonable starting estimate, expect 1 unit of NovoRapid to lower glucose by 1.7-2.8 mmol/L (30-50 mg/dL) in most adults. However, this must be individualized through careful monitoring and dose adjustment, with more conservative estimates (less glucose drop per unit) used in elderly, renally impaired, or insulin-sensitive patients to minimize hypoglycemia risk.