Converting from 70/30 Insulin to Lantus: Dosing Strategy
When switching from 160 units daily of 70/30 insulin to Lantus, start with approximately 90 units once daily (roughly 55-60% of the total 70/30 dose), as the 70/30 formulation contains 30% rapid-acting insulin that will be eliminated in the conversion. 1, 2
Rationale for Dose Calculation
- The 70/30 insulin formulation contains 70% basal (NPH) and 30% rapid-acting components, meaning only the basal portion should be converted to Lantus 1, 2
- When converting from premixed insulin to basal-only insulin, the American Diabetes Association recommends using approximately 80% of the total daily dose as a starting point for basal insulin 2
- For 160 units of 70/30 daily, this translates to approximately 128 units using the 80% rule, but a more conservative approach of 90-100 units (55-60% of total dose) is safer initially given the elimination of the prandial component 2
Critical Considerations When Switching
Eliminating the 30% rapid-acting component (approximately 48 units daily) means you will lose postprandial glucose coverage, requiring close monitoring and likely addition of mealtime insulin or a GLP-1 receptor agonist if HbA1c remains above target. 2
- The risk of nocturnal hypoglycemia should decrease with Lantus compared to 70/30 insulin, but if hypoglycemia occurs during titration, reduce the dose by 10-20% immediately 2
- Continue metformin throughout the transition unless contraindicated, as this combination provides superior glycemic control with reduced insulin requirements 3, 1
- Discontinue sulfonylureas when transitioning to prevent additive hypoglycemia risk 1
Titration Strategy
Increase Lantus by 2-4 units every 3 days based on fasting glucose readings until reaching target of 80-130 mg/dL, rather than waiting for severe hyperglycemia. 3, 2
- If fasting glucose is 140-179 mg/dL, increase by 2 units every 3 days 3
- If fasting glucose is ≥180 mg/dL, increase by 4 units every 3 days 3
- Daily fasting blood glucose monitoring is essential during titration 3
When to Add Prandial Coverage
When Lantus dose exceeds 0.5 units/kg/day (approximately 90-100 units for most adults) and postprandial glucose remains elevated, add rapid-acting insulin before the largest meal starting at 4 units, or consider a GLP-1 receptor agonist for postprandial control with weight loss benefits. 3, 2
- Start prandial insulin with 4 units of rapid-acting insulin before the largest meal, or use 10% of the current basal dose 3
- GLP-1 receptor agonists provide comparable HbA1c reduction with lower hypoglycemia risk and weight loss rather than weight gain 2
Common Pitfalls to Avoid
- Starting too conservatively when switching from premixed insulin leads to prolonged hyperglycemia and delayed achievement of glycemic targets 2
- Do not continue escalating Lantus beyond 0.5-1.0 units/kg/day without addressing postprandial hyperglycemia, as this causes overbasalization with increased hypoglycemia risk 3
- Monitor for signs of overbasalization: bedtime-to-morning glucose differential ≥50 mg/dL, hypoglycemia, and high glucose variability 3