The Difference Between U-40 & U-100 Insulin Syringes

Both insulin and the syringes used to administer insulin are expressed in units of measure as a U. The syringes are calibrated to match the same unit on the insulin bottle for ease of use. When using a syringe with a different unit calibration, you must calculate how much insulin your pet needs.

The "U" on both the insulin bottle and the syringe designates the units of active insulin. A bottle of U-100 insulin has 100 units of active insulin in each mL of the liquid. A bottle of U-40 insulin contains 40 units of active insulin in each mL.

This information translates to the same volume of U-100 insulin having 2.5 more units in it than U-40 insulin.

Each insulin syringe has the size stamped on it. Both U-100 and U-40 have the size on them. When you use the insulin and the syringe both in U-100 or U-40, you simply draw up the insulin into the syringe to the line of the appropriate units on the insulin bottle.

Some pet parents use a U-100 syringe with U-40 insulin, because the U-100 syringes are readily available at pharmacies and they have a very thin needle. The larger the number on the gauge of a needle, the thinner the needle. In this case, a conversion is necessary to supply the patient with the correct amount of insulin units.

Calculate the amount of U-40 insulin administered in a U-100 syringe by multiplying the amount of units on the insulin bottle times 2.5. Draw that amount into the U-100 insulin syringe. For example, if your pet's prescription is for 6 units of U-40 insulin, 6 x 2.5= 15. Draw up the insulin in the U-100 syringe to the 15 unit marking.