The Effect of Temperature on the Stability of In-Use Insulin Pens.

Background: Improper storage of insulin could decrease its potency. Manufacturers recommend that in-use insulin pens should be kept at between 25-30°C, but room temperature in tropical countries often exceeds this range. This study investigates the effect of temperature on the stability of basal insulin in cartridges 28 days after opening.
Methods: Four different basal insulins were evaluated. Five opened pens of each insulin type were included for each of three storage conditions and 5 unopened insulin pens of each type were stored in the refrigerator as a control. The opened pens were stored for 28 days in either a refrigerator (2-8 °C), at room temperature, or in an incubator (37 °C). Each day insulin pens were mixed 20 times and 2 units were discarded to mimic daily usage. Insulin quantity was evaluated using an ultra-high-performance liquid chromatography assay.
Results: The average room temperature during the study period was 29.7 °C. After 28 days, the percentage amount of insulin stored at refrigerator, room temperature or incubator, compared with control was 99.0, 99.7, 101.1% for long-acting insulin; 97.4, 97.2, 99.0% for NPH-1; 101.4, 101.5, 100.7% for NPH-2; and 98.7, 97.8, 98.5% for NPH-3. There were no statistically significant differences. However, we observed a trend toward different stability between clear insulin analog and turbid NPH insulin.
Conclusions: Temperature as high as 37°C and cyclic temperature,had no effect on the stability of in-use insulin pen.
Competing Interests: This research project was supported by Faculty of Medicine Siriraj Hospital, Mahidol University, Grant Number R016032029. The study sponsor was not involved in the design of the study; the collection, analysis and interpretation of data; writing the report; or the decision to submit the report for publication. The authors had no commercial associations that might create a conflict of interest in connection with this article.
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