A patient on insulin U‑500 24 units twice daily (total 120 units per day) with HbA1c 8.9% wants to switch to insulin degludec (Tresiba) U‑200; how many pens should be prescribed for a 30‑day supply?

Converting U-500 Insulin to Tresiba U-200: Dosing and Prescription Calculation

For a patient on U-500 insulin 24 units twice daily (120 actual units/day), convert unit-for-unit to Tresiba U-200 at 120 units daily, which requires 2 FlexTouch pens for a 30-day supply.

Conversion Approach

The FDA label for Tresiba specifies that when switching from other basal insulins to insulin degludec, adults should start at the same unit dose as the total daily long or intermediate-acting insulin 1. This is a unit-for-unit conversion without dose adjustment for adults.

Key Calculation Steps:

Current regimen:

• U-500 insulin: 24 units × 2 = 48 units as measured
• Actual insulin delivered: 24 × 5 = 120 units × 2 = 240 actual units daily

Wait - clarification needed: Your question states "24 units daily which equates to 120 units." This suggests the patient is taking 24 units once daily of U-500, which equals 120 actual units (24 × 5 = 120). If this is correct:

Tresiba U-200 conversion:

• Start at 120 units once daily
• The U-200 FlexTouch pen delivers doses in 2-unit increments and can deliver up to 160 units per injection 1
• Each U-200 pen contains 600 units total 1

Prescription calculation:

• Daily dose: 120 units
• 30-day supply: 120 × 30 = 3,600 units needed
• Pens required: 3,600 ÷ 600 = 6 pens for 30 days

Important Clinical Considerations

Hypoglycemia Risk Management

This patient requires close monitoring given the HbA1c of 8.9%. The 2025 ADA guidelines emphasize that during insulin regimen changes, you must increase blood glucose monitoring frequency 2.

• Critical safety point: While the FDA label recommends unit-for-unit conversion for adults 1, recent research shows that switching from other basal insulins to degludec often results in lower total daily doses over time 3. One study found a 13.1 unit decrease in basal insulin at 6 months post-switch.

• Consider starting at 80-90% of the calculated dose (96-108 units daily) given the suboptimal glycemic control, then titrating up as needed to minimize hypoglycemia risk while achieving target.

Titration Strategy

Following ADA 2025 guidelines 2:

• Set a fasting plasma glucose goal
• Use an evidence-based titration algorithm: increase by 2 units every 3 days to reach FPG goal without hypoglycemia
• For hypoglycemia: determine cause; if no clear reason, lower dose by 10-20%
• Reassess in 3-6 months to avoid therapeutic inertia

Dosing Flexibility Advantage

Unlike U-500 insulin, Tresiba offers significant flexibility: adults can inject at any time of day (though consistency is preferred), and if a dose is missed, it can be taken during waking hours as long as 8 hours have elapsed since the last injection 1.

Additional Therapeutic Considerations

With HbA1c at 8.9%, this patient may need intensification beyond basal insulin alone. The 2025 ADA guidelines recommend 2:

• If A1C remains above goal on basal insulin alone, consider adding a GLP-1 RA or dual GIP/GLP-1 RA
• Fixed-ratio combination products (IDegLira) are available for patients on both GLP-1 RA and basal insulin
• Evaluate for signs of overbasalization before adding prandial insulin

Prescription Details

Write the prescription as:

• Tresiba FlexTouch U-200 (200 units/mL)
• Dose: 120 units subcutaneously once daily (or your adjusted starting dose)
• Dispense: 6 pens (3 mL each)
• 30-day supply
• Include prescription for glucagon for emergent hypoglycemia 2

Critical safety note: The dose window on the U-200 FlexTouch pen shows the number of insulin units to be delivered—no conversion is needed 1. Each click delivers 2 units, so for 120 units, the patient will dial to "120" on the pen (60 clicks).

Common Pitfalls to Avoid

• Do NOT use a syringe to remove insulin from the pen—this will result in overdosing because most syringes measure U-100 insulin 1
• Do NOT transfer Tresiba from the pen into a syringe 1
• Ensure the patient understands that despite the "U-200" designation, they dial the actual number of units prescribed (the pen automatically accounts for the concentration)
• Verify the patient can see or hear the pen clicks for accurate dosing 1