Humulin R is the brand name for regular human insulin. It comes in two different concentrations including 100 units of insulin per 1 mL (U-100) and 500 units of insulin per 1 mL (U-500). The U-500 insulin is five times more potent than U-100 insulin and should only be used in patients requiring doses above 200 units a day.
Since U-500 insulin is not as commonly used as U-100 insulin, some healthcare professionals may not as familiar with it. This increases the chance of dispensing errors in which the U-100 and U-500 insulins may be mixed up. If this occurs, it can result in very dangerous low blood sugar or very high blood sugar levels. A mix-up between the two insulin concentrations may occur if doctors or pharmacists select the wrong concentration (for example, selecting the U-500 insulin from computer screen instead of U-100). Sometimes the two concentrations appear one line apart on the computer screen, which sets up the possibility of selection errors. Depending on the screen size, the prescriber may see only the first few words of the product listing, so the drug concentration may not be seen. In addition, the prescriber or pharmacist may assume the person needs U-100 insulin and may not even look at the concentration displayed on the screen.
A mix-up may also occur if U-100 insulin and U-500 insulin are stored next to each other on the pharmacy shelf. Although the colors of the vials are different, if someone is not aware to look for the concentration on the vials, the vials could be confused for one another.
U-500 insulin can be administered by using a prefilled insulin pen (Humulin R U-500 KwikPen) or by using a vial and a syringe to inject the insulin.
The prefilled insulin pen (Figure 1a) measures the concentrated insulin in 5-unit segments. The actual dose you want to inject is displayed in the dosing window (Figure 1b).
Figure 1a and 1b. The prefilled Humulin R U-500 insulin pen (Figure 1a) measures the concentrated insulin in 5-unit segments. The dose is displayed (circled in red) in the dosing window (Figure 1b).
If you are using Humulin R U-500 in a vial, you should only use a U-500 syringe available from the manufacturer, BD. The syringe measures U-500 insulin doses ranging from 25 units to 250 units in 5-unit segments. You should never use another type of syringe (i.e., U-100 syringe) to measure a dose of U-500 insulin. People have done this in the past and it has led to serious insulin dosing errors. If you are given a prescription for U-500 and received the medicine in vials, only use U-500 insulin syringes to prepare and administer a dose. Ask your pharmacist to provide them. Also, be sure you know how to correctly draw the prescribed dose into the U-500 insulin syringe by demonstrating to your pharmacist, diabetes educator, or doctor.
Individuals who use insulin must be aware of the concentration and insulin type that they are using. If you see U-500 on the label when you are supposed to be getting U-100, or if the opposite is true, make sure you question your pharmacist or doctor before taking it.
Also, if another individual in your home uses insulin that is not the same concentration as yours, store the insulin in different locations. This way you will not inadvertently grab the wrong vial. Never use someone else’s insulin.
If you are to be hospitalized and you use U-500 insulin, be sure to clarify this with the medical staff.
