A VA Pharmacist received an order for 40 units of U-500 insulin and questioned its validity. The actual dose desired by the physician was 200 units. The physician indicated the 40 units reflected the mark on a U 100 syringe to which the patient was to draw back the plunger. This was found to be a common practice so the VA developed a system requirement which required physicians to indicate the total units/mls (Example: 200 units/.4ml) for U 500. Insulin must be in the chart and syringes calibrated in mls must be used.
As of November 2016, a new syringe to administer concentrated Humulin R U-500 (insulin regular) has been made available from the manufacturer, BD. The syringe measures U-500 insulin doses ranging from 25 units to 250 units in 5-unit segments. Prior to the release of the U-500 syringe, it was recommended to use a U-100 syringe or tuberculin syringe to administer U-500 insulin. But dosing errors frequently occurred to patients who drew doses from a vial into a U-100 or tuberculin syringe. Every unit on the U-100 syringe scale is equal to 5 units of U-500 insulin. So, a dose measuring “40” units in a U-100 syringe is really 200 units of U-500 insulin. With a tuberculin syringe, the U-500 insulin dose has to be measured in mL, not units. Both situations have led to serious insulin dosing errors. Now that a U-500 syringe is available, a U-100 syringe or tuberculin syringe should no longer be used to administer U-500 insulin in healthcare facilities or in the home.
Humulin R U-500 is also available in a prefilled pen, which also measures the concentrated insulin in 5-unit segments. With the Humulin R U-500 KwikPen, and now with the U-500 insulin syringe, the actual dose of U-500 insulin prescribed is the actual dose that is measured in the syringe or dialed with the pen. The updated information for physicians who prescribe Humulin R U-500 now requires all prescriptions for the U-500 insulin vials to be accompanied by prescriptions for the new U-500 insulin syringes. The updated information also recommends that healthcare providers:
- Instruct patients who use vials of U-500 to use only a U-500 insulin syringe
- Teach patients how to correctly draw the prescribed dose into the U-500 insulin syringe
- Confirm that the patient has understood the directions
Bottom Line: Always indicate the dose with the words “unit markings” as this clears up the question of how much insulin to put in the syringe.
Calibrating Insulin Correctly
Originally submitted by Keith Trettin, R. Ph., MBA; updated 2019 by Steve Freed.
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