The review included 17 studies in 22 published articles and additional unpublished information from major insulin manufacturers. The data suggest it is possible to store unopened short- and intermediate-acting human insulin vials, pens/cartridges or prefilled plastic syringes at temperatures up to 25 °C (77 °F) for a maximum of 6 months and up to 37 °C (98.6 °F) for a maximum of 2 months without a clinically relevant loss of insulin potency.
Two studies found small decrements in potency at higher temperatures and/or longer durations unrefrigerated, but the rest did not.
This contrasts with current guidance and labeling that advises storing unopened human insulin at temperatures between 2 °C (35.6 °F) and 8°C (46.4 °F), necessitating refrigeration. Once the vial or pen cartridge is opened, the guidance is to store at “room temperature” and use within about 4-6 weeks.
The recommendations vary, however, and there is no clear consensus on how human insulin should be stored in settings where reliable refrigeration can’t be guaranteed, such as low-income countries, those affected by extreme heat, or areas of conflict or natural disasters. Such areas are home to growing numbers of people with diabetes, according to the Cochrane Database of Systematic Reviews report, published online.
The review also found that oscillating temperatures between 25 °C (77 °F) and 37 °C (98.6 °F), typical of daytime and nighttime fluctuations in tropical countries, for up to 3 months do not result in clinically relevant loss of insulin activity for short-acting, intermediate-acting, or mixed human insulin.
“Our study opens up new possibilities for individuals living in challenging environments, where access to refrigeration is limited. By understanding the thermal stability of insulin and exploring innovative storage solutions, we can make a significant impact on the lives of those who depend on insulin for their well-being,” the study’s lead author, Bernd Richter, MD, of the Institute of General Practice, Medical Faculty of the Heinrich-Heine-University, Düsseldorf, Germany, said in a statement.
In addition, one small pilot clinical study showed that human insulin stored for 6 weeks in an unglazed clay pot with temperatures ranging between 25 °C (77 °F) and 27°C (80.6 °F) did not result in differences in plasma glucose–lowering in eight healthy volunteers, compared with refrigerator-stored insulin. “With the help of simple cooling devices for insulin storage such as clay pots, it is possible to effectively reduce high outside temperatures in many high-temperature regions of the world,” wrote Dr. Richter and colleagues Brenda Bongaerts, PhD, and Maria-Inti Metzendorf, also from Heinrich-Heine-University.
Asked to comment, Leonardo Scapozza, PhD, of the School of Pharmaceutical Sciences at the University of Geneva, Switzerland, said that these findings align with a study he published in 2021.
“Indeed ... we have done a small-scale study by analyzing the insulin coming back from the field and showing that insulin potency and stability was conserved. An extended clinical study where the insulin is submitted to varying controlled condition is not possible and ethically debatable. But an extended study where patients are given a log tag to monitor their real storage condition and the remaining samples are collected back and sent back for analysis in a specialized lab would be very good to further confirm the [conclusions],” said Dr. Scapozza, who was not part of Dr. Richter’s team on this review.
While the issue of insulin refrigeration is less urgent in higher-income countries, it does arise, as in situations where people accidentally leave their unopened insulin out of the refrigerator or when they carry backup insulin while traveling.
The Cochrane Review excluded studies of insulin analogs, used in most developed countries, but Dr. Scapozza’s study had included them. “We observed the same stability as the ones used in low-income countries.” He added that his data combined with those in the new report provide evidence that would make it “possible to better and optimally use the available insulin that is becoming more and more costly.”
Dr. Scapozza also told this news organization that after he presented his data to Médecins Sans Frontières (Doctors Without Borders), he heard from a collaborator with that group who has diabetes. “He always used his insulin for his own treatment when he was in the field working and his insulin pen was in his backpack or pocket and his treatment was working. After hearing the data, he was very happy because he got a scientific explanation why his treatment was working, whether he was in Switzerland or during his mission in the camps submitted to the same condition of storage as any other patient in low income countries.”
Dr. Richter and Dr. Scapozza report no relevant financial relationships.
A version of this article appeared on Medscape.com.