Steve Leuck, PharmD
Steve Leuck, PharmD, has been practicing both hospital and community pharmacy for over 30 years. He founded AudibleRx, in 2011, which provides Consumer Medication Information in an easy-to-listen audible format. Increased health literacy means better outcomes.
U-500 is a concentrated form of regular insulin prescribed when patients require more than 200 units of insulin each day. While regular U-100 delivers 100 units of insulin in each mL of fluid, U-500 delivers 5 times this amount, or 500 units of insulin in each mL of fluid.
Any health care professional can imagine the potential for dosing errors with the administration of this U-500 insulin.
As pharmacists know, insulin syringes are calibrated up to 100 units in a 1-mL syringe. Currently, there are no specific syringes on the market calibrated for the U-500 insulin. As a result, the same syringes used for U-100 insulin are commonly used for U-500 dosing.
Rarely is a prescription written for U-500 insulin that doesn't require clarification from a pharmacist. When physicians order 25 units of U-500 insulin, do they really mean only 25 units, which would be measured at the 5-unit calibration mark of an insulin syringe, or do they need it to be measured at the 25-unit calibration mark, which is actually 125 units?
Whenever U-500 insulin is prescribed, the directions need to include not only the actual dose of insulin, but also the volume of insulin to be administered. Ideally, this order would be written to administer 125 units of U-500 insulin (0.25 mL) measured at the 25-unit calibration mark on a standard insulin syringe.
Through advancements in electronic prescribing, drop-down menus, and electronic health records (EHRs), any order entered into a system stays until an authorized practitioner logs into the electronic chart and changes it. When pharmacists call to clarify a U-500 insulin prescription, they need to ensure it is also changed in the EHR in order to decrease the possibility of any insulin misadventures in the future.
U-500 insulin orders should always be considered a red flag and handled with the greatest attention to detail. Pharmacists need to take extra time with patients and nursing staff to ensure everyone understands the dosing considerations when measuring and administering this concentrated form of insulin.