K. F. Lunn

Objectives To evaluate sterility in refrigerated multi‐dose insulin vials through 6 months of routine aspiration. Materials and Methods Twelve vials of insulin, six of insulin glargine U100 (Lantus®, 10 mL multi‐dose vial, Sanofi, Bridgewater, NJ) containing the preservative metacresol, and six of protamine zinc insulin U40 (ProZinc®, 10 mL multi‐dose vial, Boehringer Ingelheim, Duluth, GA) containing the preservative phenol, were refrigerated and aspirated twice daily for 6 months, using a new insulin syringe each time. Three vials of each insulin type were wiped with a single‐use alcohol swab before sampling. Three times weekly, aspirated samples were inoculated in Tryptic Soy Broth enrichment media and incubated for evidence of microbial growth. Positive broth was cultured and speciated. Endpoints were microbial vial contamination (defined as three consecutive positive cultures of the same organism) and completion of the six‐month study period. Results Microbial contamination was not identified in any vial throughout the study period. A total of 454 aspirated samples were cultured, one of which exhibited non‐repeatable growth of Staphylococcus epidermidis . This vial was prematurely lost to breakage after 59 culture samples (29 after the positive growth). Clinical Significance Refrigerated phenol‐ and metacresol‐containing multi‐dose insulin products carry minimal risk for iatrogenic infection through 6 months of use, regardless of alcohol swab preparation.