What is the recommended approach for computing insulin dosage?

Insulin Dosage Computation

Starting Doses

For type 2 diabetes patients who are insulin-naive, start with 10 units once daily or 0.1-0.2 units/kg body weight of basal insulin (such as insulin glargine), administered at the same time each day. 1, 2, 3

For type 1 diabetes patients, the total daily insulin requirement is approximately 0.5 units/kg/day for metabolically stable patients, divided as 50% basal insulin and 50% prandial insulin split among three meals. 1, 2

Type 2 Diabetes Initial Dosing

• Standard initiation: 10 units once daily or 0.1-0.2 units/kg/day of basal insulin 1, 2, 3
• Severe hyperglycemia (A1C ≥9%, glucose ≥300-350 mg/dL, or symptomatic/catabolic features): Consider 0.3-0.5 units/kg/day as total daily dose, split between basal and prandial insulin 1, 2
• Continue metformin unless contraindicated, targeting 1000mg twice daily (up to 2500mg/day total) 1, 2

Type 1 Diabetes Initial Dosing

• Total daily dose: 0.4-1.0 units/kg/day, with 0.5 units/kg/day typical for metabolically stable patients 1, 2
• Distribution: Approximately 50% as basal insulin once daily, 50% as prandial insulin divided among three meals 1, 2
• Honeymoon phase: May require lower doses of 0.2-0.6 units/kg/day 2
• Puberty/pregnancy/illness: May require doses exceeding 1.0 units/kg/day 2

Titration Algorithms

Increase basal insulin by 2 units every 3 days if fasting glucose is 140-179 mg/dL, or by 4 units every 3 days if fasting glucose is ≥180 mg/dL, until reaching target fasting glucose of 80-130 mg/dL. 1, 2

Basal Insulin Titration

• Target fasting plasma glucose: 80-130 mg/dL 1, 2
• If fasting glucose 140-179 mg/dL: Increase by 2 units every 3 days 1, 2
• If fasting glucose ≥180 mg/dL: Increase by 4 units every 3 days 1, 2
• For hypoglycemia without clear cause: Reduce dose by 10-20% immediately 1, 2
• Daily fasting blood glucose monitoring is essential during titration 1, 2

Critical Threshold: When to Stop Escalating Basal 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, 2

This threshold prevents "overbasalization," which manifests as:

• Basal dose >0.5 units/kg/day 1, 2
• Bedtime-to-morning glucose differential ≥50 mg/dL 1, 2
• Hypoglycemia (aware or unaware) 1, 2
• High glucose variability 1, 2

Adding Prandial Insulin

Start with 4 units of rapid-acting insulin before the largest meal or 10% of the current basal dose, then increase by 1-2 units or 10-15% every 3 days based on postprandial glucose readings. 1, 2

Indications for Prandial Insulin

• Basal insulin optimized (fasting glucose 80-130 mg/dL) but A1C remains above target after 3-6 months 1, 2
• Basal insulin dose approaches 0.5-1.0 units/kg/day without achieving A1C goal 1, 2
• Significant postprandial glucose excursions persist 1, 2

Prandial Insulin Initiation

• Starting dose: 4 units before the largest meal OR 10% of basal dose 1, 2
• Reduce basal insulin by 4 units or 10% when adding first prandial dose 1
• Titration: Increase by 1-2 units or 10-15% twice weekly based on postprandial readings 1, 2

Advanced Insulin Calculations

Insulin Pump Parameters

For insulin pump therapy, approximately 40-60% of total daily dose should be basal delivery, with the remainder as mealtime and correction boluses. 2

• Total basal dose: 0.48 × TDD (approximately 40-50% of total daily dose) 2, 4, 5
• Carbohydrate-to-insulin ratio (CIR): 300/TDD or 2.6 × weight(lb)/TDD 2, 4, 5
• Correction factor (CF): 1500/TDD or 1700/TDD 2, 4, 5
• Mathematical relationship: 100/TBD = ICR = CF/4.5 4

Recent prospective studies suggest that traditional formulas overestimate basal insulin needs and underestimate bolus requirements 4, 6. The updated formulas above reflect these findings.

Multiple Daily Injections

For multiple daily injections with long-acting analogs, generally 50% of total daily dose should be given as basal insulin. 2

Special Populations and Situations

Hospitalized Patients

• Insulin-naive or low-dose insulin: 0.3-0.5 units/kg/day total daily dose, with half as basal insulin 2
• High-dose home insulin (≥0.6 units/kg/day): Reduce total daily dose by 20% to prevent hypoglycemia 2
• High-risk patients (elderly >65 years, renal failure, poor oral intake): Use lower doses of 0.1-0.25 units/kg/day 2

Switching Between Insulin Types

• From TOUJEO to Lantus: Start with 80% of TOUJEO dose 3
• From once-daily NPH to Lantus: Use same dose 3
• From twice-daily NPH to Lantus: Start with 80% of total NPH dose 3

Patients on Steroids

• Without diabetes: Single morning dose of NPH may be appropriate 2
• With diabetes: Add 0.1-0.3 units/kg/day glargine to usual insulin regimen 2

Common Pitfalls to Avoid

Do not delay insulin initiation in patients not achieving glycemic goals with oral medications—this therapeutic inertia causes harm. 1, 2

• Never continue escalating basal insulin beyond 0.5-1.0 units/kg/day without addressing postprandial hyperglycemia with prandial insulin 1, 2
• Do not wait longer than 3 days between basal insulin adjustments in stable patients, as this unnecessarily prolongs time to glycemic targets 2
• Never dilute or mix insulin glargine with any other insulin or solution due to its low pH 2, 3
• Do not blame missed carbohydrate coverage for fasting hyperglycemia—fasting glucose reflects basal insulin adequacy, not meal coverage 2
• Avoid using premixed insulin in hospital settings due to unacceptably high rates of iatrogenic hypoglycemia 2
• Do not adjust total daily dose daily—recalculate TDD periodically (every few weeks to months) to update carbohydrate-to-insulin ratios and correction factors 2

Monitoring Requirements

Daily fasting blood glucose monitoring is essential during titration, with A1C checked every 3 months during intensive titration. 1, 2

• Assess adequacy of insulin dose at every clinical visit 1, 2
• Look specifically for signs of overbasalization 1, 2
• Reassess and modify treatment every 3-6 months to avoid therapeutic inertia 1, 2
• During insulin regimen changes, increase frequency of blood glucose monitoring 3

Patient Education Essentials

• Recognition and treatment of hypoglycemia (treat at ≤70 mg/dL with 15 grams of fast-acting carbohydrate) 2
• Proper insulin injection technique and site rotation to prevent lipodystrophy 1, 2, 3
• Self-monitoring of blood glucose 1, 2
• "Sick day" management rules 2
• Insulin storage and handling 2
• Equip patients with self-titration algorithms based on self-monitoring of blood glucose 2