Insulin Glargine (Lantus) to NPH Conversion
When converting from Lantus 15 units to NPH insulin, the equivalent dose is 15 units of NPH, but this should be split into twice-daily dosing with approximately 2/3 (10 units) in the morning and 1/3 (5 units) in the evening to match NPH's pharmacokinetic profile.
Understanding the Conversion Rationale
The conversion between Lantus (insulin glargine) and NPH (Neutral Protamine Hagedorn) insulin requires consideration of their different pharmacokinetic profiles:
- Lantus: Long-acting insulin analog with a relatively constant 24-hour profile with no pronounced peak
- NPH: Intermediate-acting insulin with a peak effect 4-6 hours after administration and duration of 12-18 hours
Key Conversion Principles
Unit-for-unit conversion: The American Diabetes Association guidelines suggest that the total daily dose remains the same when converting between insulin types 1
Split dosing for NPH: Due to NPH's shorter duration and pronounced peak, the total daily dose should be divided:
- Morning dose: 2/3 of total (10 units)
- Evening dose: 1/3 of total (5 units)
Timing considerations: NPH insulin should be administered to synchronize its peak with periods of highest insulin need 1
Implementation Strategy
When converting from Lantus to NPH:
Calculate total daily dose: Maintain the same total daily dose (15 units)
Split the NPH dose:
- Morning dose: 10 units (2/3 of total)
- Evening dose: 5 units (1/3 of total)
Monitor closely: Check blood glucose levels frequently during the transition period, especially:
- Fasting blood glucose (to assess overnight coverage)
- Pre-meal glucose levels (to assess daytime coverage)
- 2-4 hours after NPH administration (to monitor for peak-related hypoglycemia)
Special Considerations
Hypoglycemia Risk
NPH insulin carries a higher risk of hypoglycemia compared to Lantus due to its pronounced peak action 2. Be particularly vigilant for:
- Mid-morning hypoglycemia (from morning NPH dose)
- Nocturnal hypoglycemia (from evening NPH dose)
Timing of Administration
- Morning NPH should be given before breakfast
- Evening NPH should be given at bedtime or with dinner depending on overnight glucose patterns
Steroid Use Considerations
For patients on glucocorticoid therapy, NPH insulin may be preferred as its peak action can be synchronized with steroid-induced hyperglycemia 3. In such cases:
- Administer NPH with morning steroid dose
- Consider a different split (e.g., more NPH in morning) if on once-daily morning steroids
Monitoring and Adjustment
After conversion:
- Monitor blood glucose 2-4 times daily
- Adjust NPH doses based on patterns:
- For elevated fasting glucose: Increase evening NPH
- For daytime hyperglycemia: Increase morning NPH
- For hypoglycemia: Reduce the corresponding NPH dose by 10-20%
Remember that the pharmacokinetic differences between these insulins may necessitate further dose adjustments beyond the initial conversion to achieve optimal glycemic control.