How much does 1 unit of lispro (insulin lispro) lower blood glucose levels?

How Much Does 1 Unit of Lispro Lower Blood Glucose Levels?

One unit of insulin lispro (Humalog) typically lowers blood glucose by approximately 30-50 mg/dL (1.7-2.8 mmol/L), though this effect varies significantly between individuals based on insulin sensitivity.

Factors Affecting Insulin Sensitivity

The blood glucose-lowering effect of insulin lispro depends on several key factors:

Individual Insulin Sensitivity

• Insulin Sensitivity Factor (ISF): This is an individualized measure of how much 1 unit of insulin will decrease blood glucose
• The ISF is calculated based on the Total Daily Dose (TDD) of insulin 1
• More insulin-resistant patients (such as those with type 2 diabetes) typically require higher doses (≥1 unit/kg) 1

Time of Day

• Insulin sensitivity can vary throughout the day
• Many people require more insulin per carbohydrate in the mornings due to higher levels of counter-regulatory hormones (cortisol, growth hormone) 1

Meal Composition

• The carbohydrate content of meals significantly affects insulin requirements
• Studies show lispro has a greater tendency for early postprandial hypoglycemia compared to regular insulin when carbohydrate intake is reduced 2

Clinical Applications

Insulin-to-Carbohydrate Ratios

• The carbohydrate-to-insulin ratio is defined as the amount of carbohydrate (in grams) covered by 1 unit of insulin 1
• For example, with a ratio of 1:10, one unit of insulin would cover 10 grams of carbohydrate

Correction Dosing

• When using lispro for correction of hyperglycemia, the standard starting point is:
  • 1 unit for every 50 mg/dL (2.8 mmol/L) above target in insulin-sensitive individuals
  • 1 unit for every 25 mg/dL (1.4 mmol/L) in insulin-resistant individuals

Initiating Therapy

• For patients starting on insulin therapy, basal insulin may be initiated at 10 units or 0.1-0.2 units/kg/day 1
• For prandial insulin, a starting dose of 4 units or 10% of the basal insulin dose at the largest meal is recommended 1

Clinical Evidence

Multiple studies have demonstrated the effectiveness of insulin lispro in improving postprandial glucose control:

• Insulin lispro significantly reduces 2-hour postprandial glucose concentrations compared with sulfonylureas alone (from 18.6 to 14.2 mmol/l) 3
• In patients using continuous subcutaneous insulin infusion (CSII), insulin lispro improves 1-hour postprandial blood glucose after all meals compared to regular insulin 4

Important Considerations and Pitfalls

Hypoglycemia Risk

• Due to its rapid onset of action, lispro may cause early postprandial hypoglycemia, especially with reduced carbohydrate intake 2
• Patients should monitor glucose levels frequently when switching to lispro from regular insulin

Dosing Errors

• Concentrated insulins (U-200, U-300, U-500) are available but require careful dosing to avoid errors
• Most concentrated insulins are available only in prefilled pens to minimize dosing errors 1

Insulin Stacking

• The rapid action of lispro means it has less "stacking" effect than regular insulin
• However, frequent large correction doses can still lead to hypoglycemia if not accounting for insulin on board

Remember that while these guidelines provide a starting point, regular blood glucose monitoring is essential to determine an individual's precise insulin sensitivity factor and make appropriate adjustments to insulin dosing.