How do you calculate the initial insulin dose for a patient with type 2 diabetes?

How to Calculate Insulin Dose for 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 body weight per day, then titrate by 2-4 units every 3 days until fasting glucose reaches 80-130 mg/dL. 1, 2

Initial Basal Insulin Dosing

Standard Starting Dose

• Use 10 units once daily as the simplest approach for most patients, avoiding calculation errors while providing adequate starting coverage 1, 2
• Alternatively, calculate 0.1-0.2 units/kg/day for weight-based dosing, which accounts for body size differences 1, 2
• For a 70 kg patient, this translates to 7-14 units daily, though the flat 10-unit dose is often preferred for simplicity 2

Severe Hyperglycemia Requires Higher Starting Doses

• When HbA1c ≥9% or blood glucose ≥300-350 mg/dL, consider 0.3-0.4 units/kg/day as the starting dose 1, 2
• For HbA1c ≥10-12% with symptomatic or catabolic features (weight loss, ketosis), start basal-bolus therapy immediately with 0.3-0.5 units/kg/day total, split 50% basal and 50% prandial 1, 2, 3

Continue Metformin

• Always maintain metformin therapy (unless contraindicated) when initiating insulin, as it reduces total insulin requirements and provides complementary glucose-lowering effects 1, 2

Titration Algorithm

Evidence-Based Dose Escalation

• Increase by 2 units every 3 days if fasting glucose is 140-179 mg/dL 1, 2
• Increase by 4 units every 3 days if fasting glucose is ≥180 mg/dL 1, 2
• Target fasting plasma glucose: 80-130 mg/dL 1, 2
• If hypoglycemia occurs without clear cause, reduce dose by 10-20% immediately 1, 2

Patient Self-Titration

• Empower patients with self-titration algorithms based on self-monitoring of blood glucose, which improves glycemic control 1
• Daily fasting blood glucose monitoring is essential during the titration phase 1, 2

Critical Threshold: When to Stop Escalating Basal Insulin

The 0.5 Units/kg/day Rule

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

Signs of Overbasalization

• 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
• Fasting glucose controlled but HbA1c remains elevated after 3-6 months 1, 2

Adding Prandial Insulin

When to Add Mealtime Coverage

• After 3-6 months of optimized basal insulin, if fasting glucose reaches target but HbA1c remains above goal 1, 2
• When basal insulin approaches 0.5-1.0 units/kg/day without achieving glycemic targets 1, 2

Starting Prandial Dose

• 4 units of rapid-acting insulin before the largest meal 1
• OR 10% of the basal insulin dose per meal 1
• OR 0.1 units/kg per meal if HbA1c <8% 1
• Consider decreasing basal insulin by the same amount as the starting mealtime dose to prevent hypoglycemia 1

Prandial Insulin Titration

• Increase by 1-2 units or 10-15% every 3 days based on postprandial glucose readings 1, 2
• Rapid-acting insulin analogs are preferred over regular insulin due to their quick onset of action 1

Special Populations

High-Risk Patients

• Elderly (>65 years), renal failure, or poor oral intake: Start at 0.1-0.25 units/kg/day 2, 3
• Chronic kidney disease stage 5: Lower total daily insulin by 50% 2

Youth with Type 2 Diabetes

• Start basal insulin at 0.5 units/kg/day when HbA1c >8.5% without acidosis or ketosis, in addition to metformin 2

Hospitalized Patients

• For insulin-naive or low-dose insulin patients: 0.3-0.5 units/kg/day total, with half as basal insulin 2
• For patients on high-dose home insulin (≥0.6 units/kg/day): Reduce total daily dose by 20% to prevent hypoglycemia 2

Common Pitfalls to Avoid

Critical Errors

• Never use type 1 diabetes weight-based formulas (0.4-1.0 units/kg/day) as starting doses in type 2 diabetes 2
• Failing to reduce basal insulin when adding significant prandial doses causes hypoglycemia 2
• Continuing to escalate basal insulin beyond 0.5-1.0 units/kg/day without addressing postprandial hyperglycemia leads to suboptimal control and increased hypoglycemia 1, 2
• Delaying insulin initiation in patients not achieving glycemic goals with oral medications can be harmful 2

Cost Considerations

• Although newer long-acting analogs (glargine, detemir, degludec) cause less hypoglycemia than NPH insulin, the difference is modest 1
• NPH insulin may be a more affordable option for some patients, though it requires twice-daily dosing 1
• Concentrated insulins (U-300 glargine, U-200 degludec, U-500 regular) are indicated when daily requirements exceed 200 units but may be more expensive 1

Insulin Selection

Basal Insulin Options

• Long-acting analogs (U-100 glargine, detemir): Reduce symptomatic and nocturnal hypoglycemia compared to NPH 1
• Ultra-long-acting analogs (U-300 glargine, degludec): May convey lower hypoglycemia risk compared to U-100 glargine 1
• NPH insulin: More affordable but requires twice-daily dosing and has higher hypoglycemia risk 1

Administration Guidelines

• Administer at the same time each day 2, 4
• Rotate injection sites within the same region (abdomen, thigh, deltoid) to reduce lipodystrophy risk 4
• Never dilute or mix insulin glargine with other insulins due to its low pH 2, 4
• Never administer intravenously or via insulin pump 4