ESPE Yearbook of Paediatric Endocrinology

Brief summary: The potency of insulin decreases with increasing temperatures. This pilot study compared the concentration and structure of commonly used types of insulin when exposed to high temperatures for prolonged periods of time.

Manufacturers are required to provide information on how insulin vials and cartridges should be kept by the patient. These recommendations assume that a working fridge is available and that the medicine can be protected from elevated ambient temperatures. For example, according to the manufacturer, a 3 mL glargine cartridge (Eli Lilly, Sanofi) can be used: a) until expiration date if kept unopened at 2–8 °C, b) for 31 days if kept unopened below 30 °C, or c) for 31 days if in-use and kept refrigerated or at room temperature below 30 °C.

The authors tested the potency of various types of insulin for up to 4 months in a real-world setting during the summer in India, where ambient temperature was up to 38.6 °C. Insulin was kept either in a clay pot or on the shelf in a shady part of the home. This pilot study provides reassuring data. The concentration and structure of the various types of insulin tested were found to be mostly within 5% of those found in unopened vials/cartridges kept in the fridge under optimal conditions. As acknowledged by the authors, additional data is needed to confirm that the actual glucose-lowering effect of insulin is also conserved for prolonged periods of time at higher temperatures and that it remains unaffected by ongoing use (drawing insulin once or more every day from the same vial/cartridge).

Interestingly, in September 2022, Novo Nordisk participated in the insulin prequalification program of the WHO and took this opportunity to update the recommendations for the storage of its human insulins (100 IU/mL). They can now be stored at temperatures up to 30°C for four weeks before opening (previously it was 25 °C) (https://extranet.who.int/pqweb/news/first-human-insulins-prequalified). This will prove important for children and families with diabetes living in parts of the world where the climate is hot and humid, where the power grid may not be reliable or where conflicts/war make access to insulin unpredictable. After all, the majority of children with diabetes live in low- and middle-income countries where these conditions are unfortunately too common.