A recent scientific article revealed troubling facts regarding insulin concentration in vials, cartridges and prefilled pens sold in pharmacies. The authors found that different vials of a same type of insulin (e.g., rapid-acting, NPH) sometimes had different insulin concentration levels. For instance, a 1 ml cartridge would contain less insulin units than the standard 100 units. The different concentration levels could be explained by fluctuating temperatures (or a break in the cold chain) between the manufacturing site and the pharmacy. 

In fact, none of the insulin vials that were analyzed as part of this study contained the minimum of 95 units of insulin in a 100-unit cartridge that is required by the FDA (5% variance). So, how was the insulin concentration measured? The researchers used a technique that is approved, but also increasingly criticized by the scientific community.

A similar study just came out in the United States, and the results are far less alarming. Using a more accurate method for measuring insulin concentration, the researchers found that all the vials they analyzed were within the approved standard variance of <5%.

Insulin temperature must be properly controlled

Although the results of the second study are more encouraging, the first one serves as a good reminder of proper insulin storage requirements.

• Keep all types of insulin in the refrigerator, but avoid the colder spots. It is recommended to keep it in one of the door compartments, or in a crisper drawer.

• Insulin vials and cartridges must never be exposed to frost. Frozen insulin molecules are very likely to get destroyed and become ineffective. This is why insulin should never be kept against the back wall of the refrigerator. In winter, never keep insulin in a vehicle parked outside or in the exterior pocket of your coat, for example. When you travel, don’t carry insulin in your checked luggage, since it will be exposed to frost in the baggage compartment and on the runway.

• Insulin is also heat sensitive; exposure to excessive heat might make it deteriorate slowly. Make sure you don’t leave your insulin pen above a radiator, or exposed to the sun in a parked car. If you spend a day at the beach, you can use a case that is specifically designed to protect insulin against heat.

When kept at room temperature (i.e., 20–25°C), insulin will generally maintain an adequate concentration for up to one month after you start using a vial or cartridge. Some of the latest types of insulin can be kept up to 45 days at room temperature. 

If your blood sugar stays significantly higher than usual in spite of additional boluses, and you have ruled out potential causes such as a missed injection, illness or a catheter issue, consider using a new cartridge, vial or prefilled pen.

References

• Carter, A. W., Heinemann, L. (2017). Insulin Concentration in Vials Randomly Purchased in Pharmacies in the United States: Considerable Loss in the Cold Supply Chain. Journal of Diabetes Science and Technology, 12(4), 839–841. doi: 10.1177/1932296817747292
• Garrett, T. J., Atkinson, P., Quinlivan, E. P., Ang, L., Hirsch, I. B., Laffel, L., Atkinson, M. A. (2020). Commercially Available Insulin Products Demonstrate Stability Throughout the Cold Supply Chain Across the United States. Diabetes Care, dc191941. doi: 10.2337/dc19-1941

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