Yes, she should continue taking 28 units when switching from U-100 insulin to Tresiba U-200.
The dose in units remains the same when switching between U-100 and U-200 formulations of the same insulin—only the concentration changes, not the actual dose administered. This is explicitly confirmed by the FDA label for Tresiba, which states that "Total and maximum insulin degludec exposure at steady state are comparable between TRESIBA U-100 and TRESIBA U-200 when each is administered at the same units/kg dose" 1.
Key Dosing Principle
The U-200 formulation is simply twice as concentrated as U-100, meaning:
- 28 units of U-100 = 28 units of U-200
- The volume injected will be half (0.14 mL instead of 0.28 mL), but the actual insulin dose remains identical
- The pen device automatically accounts for the concentration difference
Critical Safety Considerations
Common pitfall to avoid: Do not confuse concentration with dose. The "200" in U-200 refers to concentration (200 units per mL), not a doubling of the dose. Patients and providers sometimes mistakenly think they need to halve the dose when switching to U-200, which would result in severe underdosing.
Why U-200 exists: The concentrated formulation allows delivery of higher insulin doses in smaller injection volumes, which can improve absorption and patient comfort—particularly relevant for insulin-resistant patients requiring large doses 2. However, the actual unit dose prescribed remains unchanged during conversion.
Monitoring After Switch
While the initial dose stays at 28 units, monitor glucose closely during the first 3-4 days as Tresiba reaches steady state 1. The ultra-long duration of action (>42 hours) means:
- Steady state is achieved after 3-4 days of daily dosing
- Dose adjustments should be made cautiously with at least 3 days between changes
- The prolonged action provides more stable glucose control but requires patience during titration
Real-world evidence confirms that when patients switch from other basal insulins to ultra-long-acting formulations like Tresiba U-200, they often end up requiring slightly lower total daily doses over time (approximately 13 units less at 6 months) while achieving better HbA1c control 3. However, start with the same 28 units and titrate based on glucose response, not based on the concentration change.