Total Daily Insulin Dose Calculation
Type 1 Diabetes
For metabolically stable patients with type 1 diabetes, start with 0.5 units/kg/day as the total daily dose (TDD), divided as 40-50% basal insulin and 50-60% prandial insulin. 1, 2
Initial Dosing Algorithm
- Standard starting dose: 0.5 units/kg/day for metabolically stable patients 1, 2
- Acceptable range: 0.4-1.0 units/kg/day depending on clinical context 1, 2
- Distribution: Give 40-50% as basal insulin (once daily long-acting) and 50-60% as prandial insulin (divided among three meals) 1, 2
Special Populations Requiring Higher Doses
- Diabetic ketoacidosis presentation: Requires higher weight-based dosing than 0.5 units/kg/day immediately following presentation 1, 2
- Puberty: Approaching 1.0 units/kg/day or higher due to hormonal insulin resistance 1, 2
- Pregnancy: Requires doses exceeding 1.0 units/kg/day 2
- Acute illness: May require 40-60% increase in TDD during infections or inflammation 2, 3
Special Populations Requiring Lower Doses
- Honeymoon phase: 0.2-0.6 units/kg/day for patients with residual beta-cell function 1, 2
- Young children: May require as low as 0.2-0.6 units/kg/day 1
Practical Example
For a 70 kg adult with type 1 diabetes:
- TDD: 70 kg × 0.5 units/kg = 35 units/day 2
- Basal insulin: 35 × 0.5 = 17.5 units once daily 2
- Prandial insulin: 17.5 units divided among three meals (approximately 6 units per meal) 2
Type 2 Diabetes
For insulin-naive patients with type 2 diabetes, start with 10 units of basal insulin once daily OR 0.1-0.2 units/kg/day, continuing metformin unless contraindicated. 1, 4
Initial Basal Insulin Dosing
- Mild-to-moderate hyperglycemia (A1C <9%): 10 units once daily OR 0.1-0.2 units/kg/day 1, 4
- Severe hyperglycemia (A1C ≥9%, glucose ≥300-350 mg/dL): Consider 0.3-0.5 units/kg/day as TDD using basal-bolus regimen from the outset 1, 4
- Continue metformin: Unless contraindicated, maintain metformin at maximum tolerated dose (up to 2000-2550 mg daily) 1, 4
Titration Protocol
- Fasting glucose 140-179 mg/dL: Increase basal insulin by 2 units every 3 days 1, 4
- Fasting glucose ≥180 mg/dL: Increase basal insulin by 4 units every 3 days 1, 4
- Target fasting glucose: 80-130 mg/dL 1, 4
- Hypoglycemia management: Reduce dose by 10-20% immediately if hypoglycemia occurs without clear cause 1, 4
Critical Threshold: When to Add Prandial Insulin
When basal insulin exceeds 0.5 units/kg/day and approaches 1.0 units/kg/day, add prandial insulin rather than continuing to escalate basal insulin alone. 1, 4
Clinical signs of "overbasalization" requiring prandial insulin addition:
- Basal dose >0.5 units/kg/day 1, 4
- Bedtime-to-morning glucose differential ≥50 mg/dL 1, 4
- Hypoglycemia episodes 1, 4
- High glucose variability 1, 4
- Fasting glucose controlled but A1C remains elevated after 3-6 months 1, 4
Adding Prandial Insulin
- Starting dose: 4 units of rapid-acting insulin before the largest meal OR 10% of current basal dose 1, 4
- Titration: Increase by 1-2 units or 10-15% every 3 days based on 2-hour postprandial glucose 1, 4
- Target postprandial glucose: <180 mg/dL 1, 4
Practical Example
For a 100 kg patient with type 2 diabetes and A1C 8.5%:
- Initial basal insulin: 10 units once daily (or 10-20 units using 0.1-0.2 units/kg) 4
- Titrate aggressively: Increase by 4 units every 3 days if fasting glucose ≥180 mg/dL 4
- Critical threshold: When dose reaches 50 units (0.5 units/kg), add prandial insulin rather than continuing basal escalation 4
Hospitalized Patients
For non-critically ill hospitalized patients requiring insulin, use 0.3-0.5 units/kg/day as TDD, divided 50% basal and 50% prandial insulin. 4
Initial Dosing by Clinical Scenario
- Insulin-naive or low-dose home insulin: 0.3-0.5 units/kg/day, with half as basal insulin 4
- High-dose home insulin (≥0.6 units/kg/day): Reduce TDD by 20% upon admission to prevent hypoglycemia 4
- High-risk patients (elderly >65 years, renal failure, poor oral intake): Use lower doses of 0.1-0.25 units/kg/day 4
Poor Oral Intake Adjustment
- Immediately reduce TDD to 0.1-0.15 units/kg/day given primarily as basal insulin, with correctional insulin only for glucose >180 mg/dL 4
- Continue basal insulin coverage even with minimal intake rather than relying solely on correction doses 4
Common Pitfalls to Avoid
- Never delay insulin initiation in patients not achieving glycemic goals with oral medications—this prolongs hyperglycemia exposure and increases complication risk 1, 4
- Never discontinue metformin when starting insulin unless contraindicated—this leads to higher insulin requirements and more weight gain 1, 4
- Never continue escalating basal insulin beyond 0.5-1.0 units/kg/day without addressing postprandial hyperglycemia—this causes overbasalization with increased hypoglycemia risk 1, 4
- Never use sliding scale insulin as monotherapy—it treats hyperglycemia reactively rather than preventing it, leading to dangerous glucose fluctuations 4
- Never give rapid-acting insulin at bedtime—this significantly increases nocturnal hypoglycemia risk 4
Advanced Calculations for Insulin Pumps
For patients using continuous subcutaneous insulin infusion:
- Total basal dose: Approximately 30-50% of TDD (not the previously recommended 50%) 4, 5
- Carbohydrate-to-insulin ratio (CIR): 300/TDD for breakfast; 400/TDD for lunch and dinner 6, 5
- Insulin sensitivity factor (ISF): 1500/TDD 4, 5
These formulas reflect updated evidence showing that previous calculations overestimated basal insulin requirements and underestimated bolus doses 5.
Special Considerations
Chronic Kidney Disease
- CKD Stage 5 with type 2 diabetes: Reduce TDD by 50% 4
- CKD Stage 5 with type 1 diabetes: Reduce TDD by 35-40% 4
Glucocorticoid Therapy
- Increase prandial and correction insulin by 40-60% or more in addition to basal insulin for patients on steroids 4, 3