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

Abstract

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.