What is the best approach for switching an adult patient with type 2 diabetes from Humulin (human insulin) to Lantus (insulin glargine)?

Switching from Humulin to Lantus: Direct Conversion Protocol

For patients switching from Humulin (human insulin) to Lantus (insulin glargine), convert the total daily basal insulin dose on a 1:1 unit basis, administered once daily at the same time each day, with dose reductions of 10-20% for high-risk patients. 1, 2, 3

Standard Conversion Algorithm

Step 1: Calculate Total Daily Basal Dose

• Add up all daily doses of Humulin N (NPH) to determine the total daily basal insulin requirement 2, 3
• If the patient is on Humulin R (regular insulin) only, this conversion does not apply—basal insulin must be initiated separately using standard starting doses 1

Step 2: Apply Conversion Ratio

• Convert unit-for-unit (1:1 ratio) from total daily Humulin N to Lantus for standard-risk patients 2, 3
• Reduce the converted dose by 10-20% for high-risk patients including: 2, 3
  • Elderly patients (>65 years)
  • Patients with renal impairment
  • History of severe hypoglycemia
  • Poor oral intake or acute illness
  • Patients previously on twice-daily NPH regimens

Step 3: Determine Administration Schedule

• Administer Lantus once daily at the same time each day, typically at bedtime or with the evening meal 1, 3, 4
• The timing can be flexible but must remain consistent day-to-day 5

Practical Conversion Examples

Example 1: Standard-Risk Patient

• Patient on Humulin N 20 units twice daily (total 40 units/day)
• Convert to Lantus 40 units once daily 2, 3

Example 2: High-Risk Patient

• Elderly patient on Humulin N 15 units twice daily (total 30 units/day)
• Reduce by 20%: 30 units × 0.8 = 24 units
• Start Lantus 24 units once daily 2, 3

Post-Conversion Monitoring Protocol

Immediate Monitoring (First 1-2 Weeks)

• Check fasting blood glucose daily to assess adequacy of the new basal dose 2, 3
• Adjust dose every 3 days based on fasting glucose patterns: 1, 3
  • If fasting glucose 140-179 mg/dL: increase by 2 units
  • If fasting glucose ≥180 mg/dL: increase by 4 units
  • Target fasting glucose: 80-130 mg/dL

Hypoglycemia Management

• If hypoglycemia occurs, reduce dose immediately by 10-20% and reassess the conversion 1, 2, 3
• Determine the cause before making further adjustments 1

Critical Considerations for Combination Therapy

Continuing Oral Medications

• Continue metformin unless contraindicated when switching to or intensifying basal insulin 6, 1
• Reassess sulfonylureas and meglitinides to minimize hypoglycemia risk, particularly if advancing beyond basal-only therapy 6

Prandial Insulin Coverage

• If the patient was on premixed insulin (Humulin 70/30), this requires a different approach 7
• The basal component should be converted as above, but prandial insulin must be added separately using rapid-acting insulin before meals 1
• Start with 4 units of rapid-acting insulin before the largest meal, or use 10% of the basal dose 1

Important Warnings and Pitfalls

Do NOT Mix or Dilute Lantus

• Never mix Lantus with any other insulin or solution due to its low pH diluent (pH 4.0) 3, 4, 5
• This requires separate injections when combining basal and prandial insulin 1

Recognize When Basal Insulin Alone Is Insufficient

• Monitor for signs of overbasalization when doses exceed 0.5 units/kg/day: 1
  • Bedtime-to-morning glucose differential ≥50 mg/dL
  • Persistent hypoglycemia
  • High glucose variability
  • Fasting glucose controlled but HbA1c remains elevated

Avoid Therapeutic Inertia

• Do not delay dose adjustments—titrate every 3 days during the conversion period 1, 3
• Reassess therapy every 3-6 months once stable to avoid prolonged suboptimal control 1

Expected Outcomes

Glycemic Control

• Lantus provides equivalent HbA1c reduction compared to NPH insulin with similar overall glycemic control 4, 8, 9
• Fasting blood glucose levels typically improve more with Lantus than with NPH insulin, especially in patients previously on twice-daily NPH 8, 9

Hypoglycemia Risk

• Significantly lower incidence of nocturnal hypoglycemia with Lantus compared to NPH insulin, while maintaining similar glycemic control 8, 9
• This benefit is particularly pronounced in patients previously on once-daily NPH regimens 8

Pharmacokinetic Advantages

• Lantus provides relatively constant basal insulin levels over 24 hours without pronounced peaks, unlike NPH insulin which has a distinct peak 4-6 hours after injection 8, 5, 9
• Improved reproducibility of plasma insulin levels compared to NPH insulin 5