Prescription Calculation for Omnipod Insulin Pump
For a patient using 70 units of Novolog (insulin aspart U-100) daily via Omnipod pump, prescribe 21 mL for a 30-day supply.
Calculation Breakdown
Since Novolog comes as U-100 concentration (100 units per mL) 1, the math is straightforward:
- Daily requirement: 70 units/day
- 30-day requirement: 70 units × 30 days = 2,100 units total
- Volume needed: 2,100 units ÷ 100 units/mL = 21 mL
Practical Prescribing Considerations
Account for waste and priming: The Omnipod system holds up to 200 units per Pod 2 and requires priming with each Pod change (typically every 2-3 days). Each Pod change wastes approximately 3-13 units during the automated cannula insertion and priming process 2, 3.
Build in a safety margin: I recommend prescribing 22-23 mL (one extra 3 mL vial) to account for:
- Pod priming losses (approximately 10-15 Pods per month = 30-195 units wasted)
- Potential Pod failures requiring early replacement
- Dose adjustments during the month
Available Formulations
Novolog (insulin aspart) U-100 is available as 1:
- 10 mL vials (most cost-effective for pump users)
- 3 mL PenFill cartridges (not compatible with Omnipod)
- 3 mL FlexPen (not compatible with Omnipod)
Prescribe: Three 10 mL vials to provide adequate supply with minimal waste, or Eight 3 mL vials if 10 mL vials are unavailable (though this is less economical).
Critical Safety Points
Pod capacity limits: Each Omnipod holds a maximum of 200 units 2. At 70 units/day, patients will need to change Pods approximately every 2.5-3 days, requiring roughly 10-12 Pods per month.
Insulin stability: While insulin aspart maintains potency when stored properly 1, patients should be counseled that insulin left in a discarded Pod (typically 20-50 units) cannot be recovered and represents expected waste inherent to pump therapy.
Verify pump settings: Ensure the pump is programmed correctly, as dosing errors can occur with concentrated insulin formulations, though this is not a concern with standard U-100 4.