Diabetes Forecast

Why is my blood glucose higher when I reach the end of my insulin vial?

Craig Williams, PharmD, responds

Insulin is a small protein, and while it is generally very stable when stored and used correctly, improper storage and handling can affect its potency. Insulin may lose potency over time once you start using a vial, even before its expiration date. This is more of a problem with vials than pens because vials hold more insulin and are therefore in use longer.

What To Know

Once you open a vial, the insulin should be good for 28 to 42 days, depending on the brand and type. A 10-milliliter vial holds 1,000 units of U-100 insulin. At 20 to 30 units per day, the vial will last 30 to 50 days. If your daily insulin dose is low, your vial may be in use longer than recommended, and the insulin may begin to lose potency near the end of the vial.

Insulin pens, on the other hand, hold less insulin. In most cases, the insulin will be used up before it starts to lose potency.

Find Out More

To find out how many days your insulin should last once the vial has been opened, check the instruction sheet that comes with your insulin, ask your pharmacist, or call the company that makes your insulin. Keep in mind:

  1. Unopened vials and pens, or your pen’s refill cartridge, should be stored in a refrigerator that’s kept at 36 to 46 degrees Fahrenheit. This helps maintain the stability of the insulin.
  2. Do not freeze your insulin, and don’t use insulin that has been partly or completely frozen.
  3. Keep insulin out of extreme heat (temperatures above 86 degrees) and avoid prolonged exposure to sunlight.
  4. Discard unopened vials that have been stored at room temperature after about a month.

You might wonder whether your insulin will retain its potency if you keep your in-use vial in the fridge. It won’t make enough of a difference. Insulin that’s room temperature stings less, so you might as well store your in-use vial at room temperature.


If your vials regularly have insulin left after their recommended in-use time, ask your provider about a smaller, 5-milliliter vial size.

Craig Williams, PharmD, is a clinical professor of pharmacy at Oregon State University/Oregon Health and Science University College of Pharmacy in Portland and an associate editor of Diabetes Forecast magazine.



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