Converting from Tresiba 15 Units to Lantus
For a patient taking 15 units of Tresiba (insulin degludec), start Lantus (insulin glargine) at 15 units once daily—use a 1:1 unit-for-unit conversion. 1, 2
Conversion Rationale
The standard approach is a direct 1:1 unit conversion when switching between long-acting basal insulins. 1, 2 Both Tresiba and Lantus are long-acting basal insulins designed to provide 24-hour glucose control, though they differ in their pharmacokinetic profiles. 3, 4, 5
Key Pharmacokinetic Differences to Understand
Tresiba (insulin degludec) has an ultra-long half-life of 17-21 hours with a duration of action exceeding 42 hours, providing extremely flat and predictable insulin levels. 5
Lantus (insulin glargine) has a shorter duration of approximately 24 hours with a peakless profile, though some patients may require twice-daily dosing if coverage is inadequate. 3, 4
Despite these pharmacokinetic differences, the glucose-lowering potency per unit is equivalent, justifying the 1:1 conversion. 5
Practical Conversion Protocol
Day 1 of Conversion
- Give the last dose of Tresiba at the usual time. 1
- Start Lantus 15 units the following day at your preferred consistent time (morning or evening). 2, 3
- Continue all other diabetes medications unchanged unless specifically contraindicated. 2
Monitoring Requirements During Transition
- Check fasting blood glucose daily for the first 2 weeks after conversion. 2
- Monitor for hypoglycemia, particularly during the first 3-5 days when residual Tresiba activity overlaps with new Lantus dosing. 5
- Watch for signs of inadequate basal coverage, including fasting glucose >130 mg/dL or significant glucose rise between meals. 2
Dose Titration After Conversion
- If fasting glucose is 140-179 mg/dL, increase Lantus by 2 units every 3 days. 2
- If fasting glucose is ≥180 mg/dL, increase Lantus by 4 units every 3 days. 2
- Target fasting glucose of 80-130 mg/dL. 2
- If hypoglycemia occurs without clear cause, reduce the dose by 10-20% immediately. 2
Critical Threshold Warning
When Lantus dose exceeds 0.5 units/kg/day (approximately 35-40 units for a 70-80 kg patient) and glucose remains elevated, this signals the need for prandial insulin coverage rather than further basal insulin increases. 2 Signs of "overbasalization" include bedtime-to-morning glucose differential ≥50 mg/dL, hypoglycemia episodes, and high glucose variability. 2
Special Considerations
Potential Need for Twice-Daily Lantus
Some patients may find that Lantus does not provide full 24-hour coverage, particularly those with type 1 diabetes or high glycemic variability. 6 If fasting glucose is controlled but pre-dinner glucose rises significantly, consider splitting the total daily Lantus dose into two administrations 12 hours apart. 6
Advantages Lost with Conversion
Tresiba's ultra-long duration allows flexible dosing timing (intervals of 8-40 hours between doses), which is lost with Lantus requiring consistent daily timing. 7, 5 However, Lantus has decades of safety data and lower cost in many settings. 3, 4
When NOT to Convert
If the patient is achieving excellent glycemic control on Tresiba 15 units without hypoglycemia, there is no clinical benefit to switching to Lantus. 6 The conversion should only be pursued for cost considerations, formulary restrictions, or patient preference. 2