Safety of Refrigerated Multidose Insulin Over 6 Months

ArticleLast Updated November 20232 min read
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Berg AS, Jacob ME, Mamo LB, Pluta DH, Lunn KF. Refrigerated multi-dose insulin vials remain sterile through 6 months of use. J Small Anim Pract. 2023. doi:10.1111/jsap.13664

Research Note

Duration-of-use recommendations for insulin are variable and inconsistent and can result in waste of insulin leftover at the time of recommended disposal, impacting pet owner costs.

This study investigated the sterility of refrigerated multidose insulin vials through 6 months of routine aspiration. Three 10-mL multidose vials each of insulin glargine U100 containing the preservative metacresol and protamine zinc insulin U40 containing the preservative phenol were stored in a standard home refrigerator (35°F-39°F [1.7°C-3.9°C]) and aspirated twice daily for 6 months. A new insulin syringe was used for each aspiration. Half of the bottles were wiped with a single-use alcohol swab before each aspiration. Samples from each vial were cultured for growth 3 times weekly.

No evidence of microbial contamination was noted. Nonrepeatable growth of a single Staphylococcus epidermidis isolate from one vial was attributed to secondary contamination during transport or laboratory handling. Results suggest bacterial contamination of insulin glargine U100 or protamine zinc insulin U40 is unlikely with 6 months of routine, twice-daily use when refrigerated in a home environment and always aspirated using a new sterile syringe.