Insulin Pen Supply Calculation for 90-Day Period
For a patient taking 50 units of insulin daily using 1.5 mL pens containing 300 units/mL, you need to dispense 10 pens for a 90-day supply.
Calculation Breakdown
Step 1: Determine Total Units Per Pen
- Each pen contains 1.5 mL at a concentration of 300 units/mL 1
- Total units per pen = 1.5 mL × 300 units/mL = 450 units per pen 1
Step 2: Calculate Total Insulin Needed for 90 Days
Step 3: Calculate Number of Pens Required
- Number of pens = 4,500 units ÷ 450 units per pen = 10 pens exactly 1
Practical Considerations for Dispensing
Account for Wastage and Priming
- Some insulin remains in the pen after the last full dose is administered 1
- Priming the pen before each injection uses a small amount of insulin (typically 2 units per prime) 2, 1
- Proper injection technique may result in minor wastage 2
Recommended Prescription Approach
- Dispense 10 pens for the 90-day supply as the mathematical calculation is exact 1
- Consider adding 1 additional pen (total of 11 pens) if the patient has a history of technique issues, frequent priming needs, or if you want to provide a safety buffer 1
- Insurance coverage typically provides 30-day supplies, so this would be dispensed as approximately 3-4 pens per month 1
Important Safety Considerations
Pen Device Selection
- Insulin pens are available as disposable prefilled pens or reusable pens with replaceable cartridges 2
- For patients with dexterity issues or vision impairment, insulin pens facilitate accurate dose administration 2
Concentrated Insulin Awareness
- Standard U-100 insulin delivers 100 units/mL 3, 4
- Your patient's pen contains 300 units/mL concentration, which requires careful attention to avoid dosing errors 3, 4
- Ensure the patient understands they are dosing in units, not volume, to prevent administration errors 5, 3