Converting Lantus to NPH Insulin
When converting 20 units of Lantus (insulin glargine) to NPH insulin, start with 25 units of NPH (125% of the Lantus dose), which represents the inverse of the 80% conversion factor used when transitioning from NPH to Lantus. 1
Conversion Rationale
The guideline evidence establishes that when switching from NPH to Lantus, you use 80% of the NPH dose to reduce hypoglycemia risk during transition. 1 Therefore, when converting in the reverse direction (Lantus to NPH), you need to increase the dose proportionally:
- 20 units of Lantus ÷ 0.80 = 25 units of NPH 1
- This accounts for NPH's shorter duration of action and more pronounced peak compared to Lantus's flat, peakless profile 2, 3
Dosing Schedule Considerations
- NPH typically requires twice-daily dosing to provide adequate 24-hour basal coverage, unlike Lantus which is given once daily 1, 2
- If splitting the 25 units into twice-daily NPH, use a 2/3 morning and 1/3 evening split (approximately 17 units morning, 8 units evening) 4
- Alternatively, if using once-daily NPH, administer the full 25 units in the morning, though this provides less optimal coverage than twice-daily dosing 1
Critical Monitoring During Transition
- Monitor blood glucose more frequently during the first 1-2 weeks of transition, especially checking fasting and pre-dinner levels 1
- Watch for increased nocturnal hypoglycemia risk, as NPH has a more pronounced peak at 4-6 hours compared to Lantus's peakless profile 4, 2, 3
- If hypoglycemia occurs without clear cause, reduce the NPH dose by 10-20% 1, 5
Titration After Initial Conversion
- After establishing the initial NPH dose, titrate by 2 units every 3 days based on fasting glucose targets 1
- Assess adequacy of basal coverage at each follow-up visit 1
- Avoid abrupt changes in injection sites, as NPH absorption rates may vary between sites 1
Common Pitfalls to Avoid
- Do not use a 1:1 conversion ratio (20 units Lantus to 20 units NPH), as this will likely result in inadequate glycemic control due to NPH's shorter duration of action 1, 2
- Expect the patient to experience more variable glucose levels with NPH compared to the flat profile of Lantus 2, 3
- Be prepared to add or adjust prandial insulin coverage, as the transition may reveal previously masked postprandial hyperglycemia 1