From the FDA Drug Label
PRINCIPAL DISPLAY PANEL Levemir® Insulin detemir (rDNA origin) injection ... 100 units/mL (U-100) To determine the number of units in 0.25 mL of insulin, we need to calculate 25% of 100 units, since 0.25 mL is one-quarter of 1 mL.
- 100 units/mL * 0.25 mL = 25 units 1
From the Research
In a 1 mL insulin syringe, 0.25 mL equals 25 units, as standard insulin syringes are calibrated so that 1 mL equals 100 units, making each 0.01 mL equivalent to 1 unit. This conversion is based on the standardization of U-100 insulin, which is the most common concentration used in the United States and many other countries 2. The use of unit markings on insulin syringes is crucial for accurate dosing, rather than estimating milliliters, as the syringes are specifically designed with unit graduations for precise measurement.
Some studies have investigated the accuracy and precision of insulin administration using various devices, including syringes and pens 3, 4. However, these studies do not affect the basic conversion of milliliters to units in a standard insulin syringe. Another study discussed the use of insulin syringes to reduce dosing errors for enoxaparin, a low molecular weight heparin, by administering whole milligram doses via an insulin syringe 5. Nevertheless, this does not change the fundamental conversion of 0.25 mL to units in a 1 mL insulin syringe.
The key point to remember is that 0.25 mL in a 1 mL insulin syringe corresponds to 25 units, based on the standard calibration of these syringes. This is essential for accurate insulin dosing and applies to the most commonly used concentration of insulin, U-100.