When Precision Fails: The Hidden Issues in Insulin Pen Dosing Calculations

1. Not all pens can deliver insulin in 1-unit increments
2. Not all pens use a 2-unit prime

Let’s look at an example using Toujeo^® Max U-300 SoloStar^® Pen. Imagine a patient was prescribed 1 box (6 mL) of Toujeo^® Max with directions to inject 57 units nightly at bedtime. The pharmacy correctly determines each 6 mL box has 1,800 units. Since this pharmacy chooses to use priming units in their days’ supply calculation, they add in a 2-unit prime to their days’ supply equation. They determine 6 mL is a 30.5 days’ supply (rounding to a 30 or 31 days’ supply – either is allowable). The math is right; however, this days’ supply would be wrong!

How is it wrong? The first mistake is that Toujeo^® Max U-300 SoloStar^® can only deliver doses in 2-unit increments. Since the prescription was written for 57 units nightly, the pharmacy should have contacted the prescriber’s office to clarify the prescription to a dose which could be dialed by the Toujeo^® Max pen. Second, Toujeo^® Max uses a 4-unit prime, therefore, the assumption that it used a 2-unit prime was also wrong.

Going back to the example above, let’s figure out the correct days’ supply. In this alternate timeline, the pharmacy called the prescriber’s office and clarified the directions to inject 58 units nightly at bedtime. They documented the change within the prescription record with a full clinical note and updated the patient label with the new directions. Now, the days’ supply calculation is made using 1,800 units per box, 58 units per day plus the 4-unit prime making 6 mL a 29 days’ supply.

While the days’ supply in this scenario was only altered marginally, there can still be subsequent consequences for having the wrong days’ supply on a claim, no matter how significant the error. For example, an incorrect days’ supply could cause a patient’s copay to increase (or decrease) once corrected. Additionally, the pharmacy could receive penalty fees during an audit for an incorrect days’ supply or recoupment against the claim if there is a difference in the reimbursement or patient’s copay once the days’ supply is corrected. There could also be issues with an overbilled quantity, refill too soon, or with exceeding plan limitations which can all lead to significant recoupment.

Below is a reference table which shows insulin pens with unique dosing increments and a list of insulin pens which do not use the standard 2-unit prime.

PAAS Tips:

• Always submit an accurate days’ supply, when possible.
• Pharmacies are NOT required to use priming units in their days’ supply calculations. If priming units are included, be sure this is reflected on the hardcopy record and visible to an auditor.
• Information about which insulin pens do not follow the standard 1-unit dosing increment or 2-unit prime can also be found in the foot notes of the PAAS Insulin Medication Chart.
• A complete clinical note should include:
  • Date and time
  • Name and title of individual providing information
  • Specific information clarified
  • Pharmacy staff initials
• The patient label must be updated with the clarified directions prior to dispensing to avoid recoupment for mis-matched directions (i.e., the directions on the hardcopy don’t match the patient label).