We have serious concerns about the article, “Insulin Concentration in Vials Randomly Purchased in Pharmacies in the United States: Considerable Loss in the Cold Supply Chain,”[1] published in the Journal of Diabetes Science and Technology on December 21, 2017.

The article describes measuring insulin concentration in vials of human insulin (regular and NPH) from different pharmacies at different times of the year, from two different manufacturers. The authors report a mean potency of approximately 40 U/ml instead of the FDA-mandated > 95 U/ml, with the regular human insulin alone averaging less than 25 U/ml potency and the NPH at approximately 55 U/ml.

The number of samples studied is extremely small (18 vials total) in relation to the number of vials manufactured and dispensed, and the methodology for sample handling and preparation is minimally described. More important, there are serious concerns about whether the results match real-world experience and whether appropriate testing methods were used. We have consulted with both clinical and biochemistry experts in this area. Several leading clinical experts have stated that the study’s results are inconsistent with their experience of using pharmacy-obtained insulin in controlled clinical research studies where patients are able to achieve proper blood glucose control, thus the insulin potency is clearly in-line with the labeled 100 U/ml. From a biochemistry perspective, there are concerns about the testing method used—why didn’t they use the common and readily available insulin assays normally used to measure insulin potency?

We have also been in communication with insulin manufacturers. We have reviewed and confirmed the quality control procedures that are strictly adhered to and documented by each manufacturer throughout the supply chain, from manufacturing to delivery, to meet FDA standards to ensure the safety, potency and efficacy of insulin.

Based on these findings, we have no reason to believe that the results of Carter et al.’s study reflect the actual potency of human insulin widely available at retail pharmacies in the United States. We strongly urge patients to talk with their doctors and pharmacists about any concerns they have with their insulin or diabetes treatment plan.

—William T. Cefalu, MD, Chief Scientific, Medical and Mission Officer, American Diabetes Association

[1] Carter, AW and Heinemann, L. 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. https://doi.org/10.1177/1932296817747292