Background: Improper storage of in use insulin could decrease its potency. Temperature has been shown to have an effect on the stability of insulin. Therefore, the manufacturers recommend to keep an in use insulin at the room temperature (RT), not exceeding 25-30 C. However, The RT in tropical countries are higher than that. Thus far, there are few studies evaluate the effect of temperature on insulin stability, especially insulin pens which are widely used nowadays.

Aim: To investigate the effect of temperature on the stability of basal insulin after opening for 28 days.

Methods: There are four different commercial basal insulin pens, including long and intermediate acting insulin were evaluated (N=5 each). They were opened and stored at 3 different conditions, including: refrigerated (2-8 C), RT and incubator (37 C) for 28 days. An unopened insulin pens from the same batches were stored under standard condition as control (CON). During the study period, the insulin pens were well-mixed and discarded 2 units every day to mimic the daily usage of diabetes patient. The temperature logger was used to record the hourly temperature in RT. After 28 days, the amount of insulin was evaluated using the Ultra-high performance liquid chromatography assay.

Results: Average RT throughout the study period was 29.7 ± 2.8 C. The percentage amount of insulin (mean ± SD) stored at 4oC, RT or 37oC, compared with CON was as follows: 99.0 ± 0.8%, 99.7 ± 2.5%, 101.1 ± 1.2% for long-acting insulin; 97.4 ± 0.7%, 97.2 ± 1.6%, 99.0 ± 1.2% for NPH-1; 101.4 ± 1.1%, 101.5 ± 2.5%, 100.7 ± 2.3% for NPH-2; and 98.7 ± 1.5%, 97.8 ± 1.1%, 98.5 ± 1.7% for NPH-3. There was no statistically significant in the difference. However, there was a trend toward different in AUC between long acting and NPH insulin.

Conclusion: Temperature, as high as 37 C, cyclic temperature and the variability of temperature range from 4 C to room temperature had no effect on the stability of in use insulin pen. We observed the trend toward different in stability between clear insulin analog and turbid NPH insulin.


T. Kongmalai: None. L. Preechasuk: None. S. Junnu: None. S. Manocheewa: None. C. Srisawat: None. A. Sriwijitkamol: None.

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