Abstract
Strict storage recommendations for insulin are difficult to follow in hot tropical regions and even more challenging in conflict and humanitarian emergency settings, adding an extra burden to the management of people with diabetes. According to pharmacopeia unopened insulin vials must be stored in a refrigerator (2–8°C), while storage at ambient temperature (25–30°C) is usually permitted for the 4-week usage period during treatment. In the present work we address a critical question towards improving diabetes care in resource poor settings, namely whether insulin is stable and retains biological activity in tropical temperatures during a 4-week treatment period. To answer this question, temperature fluctuations were measured in Dagahaley refugee camp (Northern Kenya) using log tag recorders. Oscillating temperatures between 25 and 37°C were observed. Insulin heat stability was assessed under these specific temperatures which were precisely reproduced in the laboratory. Different commercialized formulations of insulin were quantified weekly by high performance liquid chromatography and the results showed perfect conformity to pharmacopeia guidelines, thus confirming stability over the assessment period (four weeks). Monitoring the 3D-structure of the tested insulin by circular dichroism confirmed that insulin monomer conformation did not undergo significant modifications. The measure of insulin efficiency on insulin receptor (IR) and Akt phosphorylation in hepatic cells indicated that insulin bioactivity of the samples stored at oscillating temperature during the usage period is identical to that of the samples maintained at 2–8°C. Taken together, these results indicate that insulin can be stored at such oscillating ambient temperatures for the usual four–week period of use. This enables the barrier of cold storage during use to be removed, thereby opening up the perspective for easier management of diabetes in humanitarian contexts and resource poor settings.
Highlights
Diabetes is a worldwide health issue, with the affected population estimated to reach 592 million people in 2035, representing a 55% increase over the period 2013–2035 [1]
According to pharmacopeias, reversed-phase high performance liquid chromatography (HPLC) coupled with UV detection at 214 or 280 nm is the method of choice for insulin quantification [17,19,21,25,26,27,28,29,30] and for potency determination because of the correlation that has been described between HPLC quantification and biological activity [17,18,19,21]
The analysis of the samples in which instability was forced by high temperature (80 ̊C) showed a decrease in insulin content of 9 to 14% compared to corresponding reference formulations stored at 2–8 ̊C
Summary
Diabetes is a worldwide health issue, with the affected population estimated to reach 592 million people in 2035, representing a 55% increase over the period 2013–2035 [1] This increase will be highest in low- and middle-income countries. Insulin was discovered in 1921, first administered to a patient in 1922 and included on the World Health Organization’s Model List of Essential Medicines. Access to this medicine is still problematic in many settings globally and its cost represents a large financial burden on individuals and health systems [3,4]. Most of the efforts to improve availability have been targeted at cost reduction and increased local availability of insulin [5]
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