What is the formula to adjust the dose of insulin (insulin therapy) based on glucose levels?

Insulin Dose Adjustment Formula

Adjust basal insulin by 2-4 units every 3 days based on fasting glucose: increase by 4 units if fasting glucose ≥180 mg/dL, by 2 units if 140-179 mg/dL, maintain if 80-130 mg/dL, and decrease by 2 units if more than 2 fasting values per week are <80 mg/dL. 1, 2

Basal Insulin Titration Algorithm

The American Diabetes Association provides a systematic approach to insulin adjustment based on glucose monitoring 1, 2:

• If fasting glucose ≥180 mg/dL: Increase basal insulin by 4 units every 3 days 1, 2
• If fasting glucose 140-179 mg/dL: Increase basal insulin by 2 units every 3 days 1, 2
• If fasting glucose 80-130 mg/dL: Maintain current basal insulin dose 1, 2
• If >2 fasting values per week <80 mg/dL: Decrease basal insulin by 2 units 1, 2
• If hypoglycemia occurs without clear cause: Reduce dose by 10-20% immediately 1

Critical Threshold: When to Stop Escalating Basal Insulin

Stop increasing basal insulin when the dose exceeds 0.5 units/kg/day and add prandial insulin instead, as continuing to escalate basal insulin alone leads to "overbasalization" with increased hypoglycemia risk and poor control. 1, 2

Clinical signals of overbasalization include 1:

• Basal insulin dose >0.5 units/kg/day
• Bedtime-to-morning glucose differential ≥50 mg/dL
• Hypoglycemia episodes
• High glucose variability

Prandial Insulin Adjustment Formula

When adding or adjusting prandial insulin 1, 2:

• Initial prandial dose: Start with 4 units of rapid-acting insulin before the largest meal OR 10% of current basal dose 1, 2
• Titration: Increase prandial insulin by 1-2 units or 10-15% every 3 days based on pre-meal and 2-hour postprandial glucose readings 1, 2

Advanced Formulas for Insulin Pump Users

For patients on continuous subcutaneous insulin infusion 3, 4:

• Total basal dose = TDD × 0.48 (approximately 30-50% of total daily dose) 1, 3
• Carbohydrate-to-insulin ratio (CIR):
  • Breakfast: 300/TDD 4
  • Lunch and supper: 400/TDD 4
  • Alternative formula: (2.6 × Weight in lbs)/TDD 3
• Insulin sensitivity factor (correction factor): 1500/TDD or 1960/TDD 1, 3

Initial Dosing Guidelines

For type 2 diabetes patients starting insulin: Begin with 10 units once daily or 0.1-0.2 units/kg/day 1, 2, 5

For type 1 diabetes patients: Total daily insulin typically 0.4-1.0 units/kg/day, with approximately 50% as basal insulin and 50% as prandial insulin 1, 2

For severe hyperglycemia (A1C ≥9%, glucose ≥300-350 mg/dL): Consider starting with 0.3-0.5 units/kg/day as total daily dose, split between basal and prandial insulin 1, 2

Monitoring Requirements

• Daily fasting blood glucose monitoring is essential during titration 1, 2
• Reassess every 3 days during active titration 1, 2
• Check HbA1c every 3 months during intensive titration 1
• Monitor pre-meal and 2-hour postprandial glucose when adjusting prandial insulin 1, 2

Common Pitfalls to Avoid

• Never continue escalating basal insulin beyond 0.5-1.0 units/kg/day without addressing postprandial hyperglycemia, as this leads to suboptimal control and increased hypoglycemia risk 1, 2
• Do not use sliding scale insulin as monotherapy in hospitalized patients—use scheduled basal-bolus regimens instead 6
• Do not delay adding prandial insulin when basal insulin has been optimized (fasting glucose 80-130 mg/dL) but A1C remains above target after 3-6 months 1
• Continue metformin when adding or intensifying insulin therapy unless contraindicated 1, 2

Special Considerations for CGM Users

For patients using continuous glucose monitoring with trend arrows 7:

• Adjust insulin bolus based on rate of glucose change (at least 1 mg/dL per minute)
• When preprandial trend arrow is increasing: increase bolus dose
• When preprandial trend arrow is decreasing: decrease bolus dose to prevent hypoglycemia

This approach kept subjects on target for 70.8% and 91.6% of postprandial time when preprandial trend arrows were increasing or decreasing, respectively 7