How Long Should Insulin Be Used Once a Vial Is Started?

Response to Molitch

We thank Dr. Molitch (1) for his comments in this issue of Diabetes Care regarding our previous response (2) concerning the issue of insulin stability. Dr. Molitch points out apparent differences among manufacturers in our original letter with respect to in-use recommendations, and he requests actual data on insulin potency and that insulin be provided in smaller containers. We appreciate the opportunity to comment further on these important questions.

First, we will provide storage recommendations for the Lilly insulin formulations and containers available in the U.S. Second, we will explain further why the storage guidelines vary by formulation and type of container. Third, we will provide supporting data and explanations for our recommendations.

In-use recommendations for insulins in vials differ from those for insulin in cartridges or prefilled insulin pens. Recommendations for insulin products in vials are the same regardless of the formulation. However, the in-use recommendations may differ for that formulation when the same insulin is available in a cartridge. The primary reason for the different in-use dating recommendation between vials and cartridges is based on differences in the expected use of these products. For example, insulin in cartridges is expected to undergo more rigorous agitation and exposure to more widely varying temperatures by patients than insulin in vials. The in-use dating guidelines established by the Food and Drug Administration (FDA) for cartridges take into account the smaller volume and fewer total units of insulin compared with vials, as well as the potential exposure of insulin to greater heat and mechanical agitation.

The recommended in-use dating once an insulin vial has been punctured is 28 …