U-500 Insulin Errors


Humulin R is the brand name for Eli Lilly's recombinant human regular insulin. The usual version of Humulin R is U-100 and contains 100 units of insulin activity per 1 milliliter of fluid. But there's also a rarely-used version called U-500. The U-500 insulin is 5 times more potent than U-100 insulin. U-500 insulin contains 500 units of insulin activity per 1 milliliter of fluid. People may need to use U-500 if their diabetes is not well-controlled with U-100. The U-500 version should be used only for patients requiring doses above 200 units a day.

Important information about U-500 insulin

Since the use of U-500 insulin is not as common as the use of U-100 insulin, some health professionals may not be aware of it. This by itself increases the chance of dispensing errors.

The main problem with U-500 insulin is the risk of a  mix-up between the insulin U-100 and insulin U-500 versions. If this occurs, it can result in very dangerous low blood sugar or very high blood sugar. A mix-up between the two insulin concentrations may occur if doctors or pharmacists select the wrong concentration (for example, selecting the U-500 regular 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 is not seen. Prescribers may assume the patient needs U-100 and may not even look for the concentration on the screen.

A mix-up may also occur if U-100 insulin and U-500 insulin are stored next to each other at the pharmacy, in the hospital or even in your home. Although the colors of the vials are different, if someone is is not aware to look out for the concentration on the vials, the vials could be confused for one another.

U-500 insulin for injection: syringe recommendations

Another problem associated with U-500 insulin is the potential for dosing errors when using an insulin syringe. This is because a U-500 insulin syringe does not exist.The largest insulin syringe only holds 100 units per 1 ml. This means, you would would need to divide the amount of U-500 insulin units you are prescribed by five. Using a U-100 insulin syringe to draw up U-500 insulin can be associated with some risk. For example, if you are admitted to the hospital in an emergency, you may not be able to speak for yourself. If a doctor asks a family member about what medicines you take, a family member may say "30 units of regular insulin." If the doctor does not confirm the concentration or the family member does not remember to tell the doctor U-500 insulin is being used, the doctor may assume you mean U-100 insulin and then you could receive an under dose of insulin.

Because a U-500 insulin syringe does not exist, another option for injecting U-500 insulin is by using a  tuberculin (TB) syringe. While hospitals have these available and may provide an initial supply, you may need to special order these from your pharmacy. A TB syringe will allow for accuracy when measuring this very concentrated insulin and will also lower your risk of dosing errors. TB syringes look similar to insulin syringes but instead measure in milliliters (mL) instead of units. TB syringes will also be designated with the word tuberculin on the syringe. Unlike U-100 insulin which is only prescribed in units, when a TB syringe is used, U-500 insulin is prescribed in milliliters.



Important note about a TB syringe


When using a TB syringe it is important to remember the volume of a TB syringe is always one milliliter (mL).The syringe indicates the one with a zero after a decimal point (this is also known as a "trailing zero"). It is important to understand this is the number one and not ten.

*In some circumstances, insurance companies will not cover the cost of TB syringes since they are not considered a "diabetic need." In this situation, you will need to use a U-100 syringe and do the conversion as stated earlier.

Other Recommendations

Individuals who use insulin must be aware of the concentration and insulin type that you normally use. 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 also uses insulin that is not the same concentration as yours, store the insulin in different areas. This way you will not inadvertently grab the wrong vial.

If you are to be hospitalized and you use U-500 insulin, be sure to clarify this with the medical staff. It is recommended to bring whichever syringe you use at home to the hospital and demonstrate where you normally draw up your insulin to.

Medication Safety Alerts

FDA Safety Alerts

Show Your Support!

ISMP needs your help to continue our life saving work