In an adult with diabetes, how much does one unit of injectable Mixtard (human insulin 70/30) lower blood glucose?

How Much Does One Unit of Mixtard Lower Blood Glucose?

One unit of injectable Mixtard typically lowers blood glucose by approximately 30–50 mg/dL in adults with diabetes, though this effect varies significantly based on individual insulin sensitivity, body weight, and insulin resistance. 1

Understanding the Insulin Sensitivity Factor

The glucose-lowering effect of insulin is quantified using the insulin sensitivity factor (ISF), also called the correction factor, which is individualized for each patient 1. The ISF is calculated using the formula:

• ISF = 1500 ÷ Total Daily Dose (TDD) for regular insulin 1
• ISF = 1700 ÷ TDD for rapid-acting analogs 1

Since Mixtard is a premixed formulation containing 30% regular insulin and 70% NPH, the 1500 formula is more appropriate 2, 3.

Practical Example

For a patient taking 40 units total daily insulin, the ISF would be:

• 1500 ÷ 40 = 37.5 mg/dL per unit 1

This means each unit of insulin would lower blood glucose by approximately 37.5 mg/dL in this individual 1.

Factors That Modify Insulin Sensitivity

Several critical factors influence how much one unit of Mixtard will lower blood glucose:

Body Weight and Insulin Resistance

• Patients with higher insulin resistance require more insulin to achieve the same glucose reduction 1
• Type 2 diabetes patients commonly require ≥1 unit/kg/day due to insulin resistance, substantially higher than type 1 diabetes requirements 2
• Physically active patients with stable weight often need substantially less insulin due to improved insulin sensitivity 1

Time of Day

• Morning hours often require more insulin per gram of carbohydrate due to counter-regulatory hormones like cortisol and growth hormone 1
• The dawn phenomenon can reduce insulin sensitivity in early morning hours 1

Physical Activity Level

• Exercise increases insulin sensitivity, requiring less insulin to lower glucose 1
• Regular physical activity—at least 150 minutes weekly of moderate-intensity exercise—significantly decreases insulin resistance 1

Mixtard-Specific Pharmacodynamics

Mixtard (human insulin 70/30) has distinct pharmacokinetic properties that affect its glucose-lowering capacity:

• The 30% regular insulin component provides glucose-lowering effects primarily in the first 0–8 hours after injection 4, 3
• The 70% NPH component provides intermediate-acting coverage extending beyond 8 hours 4, 3
• Peak glucose infusion rate occurs at approximately 272–313 minutes (4.5–5.2 hours) after injection 4
• Maximum serum insulin concentration (Cmax) for 70/30 premixed preparations is approximately 44–54 microU/mL at standard doses 4

Calculating Correction Doses with Mixtard

When blood glucose is above target, the correction dose can be calculated using 1:

1. Determine current blood glucose and target glucose
2. Calculate the difference (current glucose − target glucose)
3. Divide by the ISF to determine units needed

Example Calculation

• Current glucose: 250 mg/dL
• Target glucose: 120 mg/dL
• Difference: 130 mg/dL
• ISF: 40 mg/dL per unit
• Correction dose: 130 ÷ 40 = 3.25 units (round to 3 units) 1

Critical Safety Considerations

Avoid Insulin Stacking

• Do not administer correction doses within 3–5 hours of the previous dose, as insulin from the previous injection may still be active 1
• Mixtard's dual-action profile (regular + NPH) creates overlapping insulin activity that increases stacking risk 4, 3

Recalculate ISF Periodically

• The insulin sensitivity factor should be recalculated during illness, changes in physical activity patterns, or significant weight changes 1
• For patients on Mixtard, reassess ISF every 2 weeks during dose titration 2

High-Risk Populations Require Lower Doses

• Elderly patients (>65 years), those with renal impairment, or poor oral intake require lower starting doses (0.1–0.25 units/kg/day) to prevent hypoglycemia 1, 2
• Patients with severe renal impairment (CKD Stage 5) should reduce total daily insulin dose by 50% for type 2 diabetes and 35–40% for type 1 diabetes 1

Common Pitfalls to Avoid

• Do not assume a fixed "2 units lowers glucose by X mg/dL" rule—insulin sensitivity varies dramatically between individuals and clinical situations 1
• Do not use correction doses as monotherapy—scheduled basal-bolus insulin regimens are superior to sliding-scale approaches 1
• Do not give rapid-acting insulin at bedtime as a sole correction dose, as this markedly raises nocturnal hypoglycemia risk 1
• Do not continue escalating Mixtard beyond 0.5–1.0 units/kg/day without considering transition to basal-bolus therapy, as this leads to overbasalization with increased hypoglycemia risk 2

When to Transition from Mixtard

Consider transitioning from premixed Mixtard to basal-bolus therapy when 2:

• Total daily Mixtard dose exceeds 0.5 units/kg/day without achieving HbA1c goals
• Fasting glucose is controlled but HbA1c remains above target after 3–6 months
• Patient requires more precise dosing control due to unpredictable eating patterns