I have always been taught that insulin must remain in the refrigerator or it loses it's "potency." I did look up the FDA Patient Package Insert online, which says the following:
All Unopened Novolin N:
- Keep all unopened Novolin N in the refrigerator between 36° to 46°F (2° to 8°C).
- Do not freeze. Do not use Novolin N if it has been frozen.
- If refrigeration is not possible, the unopened vial may be kept at room temperature for up to 6 weeks (42 days), as long as it is kept at or below 77°F (25°C).
- Keep unopened Novolin N in the carton to protect from light.
- Keep at room temperature below 77°F (25°C) for up to 6 weeks (42 days).
- Keep vials away from direct heat or light.
- Throw away an opened vial after 6 weeks (42 days) of use, even if there is insulin left in the vial.
- Unopened vials can be used until the expiration date on the Novolin N label, if the medicine has been stored in a refrigerator.
Yes, it is fine to leave an opened NPH insulin vial at room temperature, but if left out of the refrigerator, we should discard it after 6 weeks (1-3). In extremely hot climates, it has been recommended that the vial be replaced even more frequently if left unrefrigerated (4). Storing the insulin in the fridge helps maintain insulin potency, allowing one to use that opened vial for up to 4 to 6 months.
I don't know too many owners that would think leaving it out of the refrigerator is worth the added cost of purchasing more insulin. But that is the owner's choice.
I can think of only one downside for storing insulin in the refrigerator —injecting cold insulin can sometimes make the injection more painful. To avoid this, one can draw up the insulin and wait a couple of minutes before injection, making sure that the insulin is not too cold injected. Or one could roll the syringe between the palms of both hands for 30-60 seconds (with the needle facing upward) just prior to injecting to remove the "chill."
- Insulin Storage and Syringe Safety. American Diabetes Association website. http://www.diabetes.org/living-with-diabetes/treatment-and-care/medication/insulin/insulin-storage-and-syringe.html
- Guide for Storage of Insulin. Wisconsin Department of Health Services. http://www.dhs.wisconsin.gov/rl_dsl/publications/GudStrgInsulin.pdf
- Grajower MM, Fraser CG, Holcombe JH, et al. How long should insulin be used once a vial is started? Diabetes Care 2003;26:2665-2666.
- Vimalavathini R, Gitanjali B. Effect of temperature on the potency & pharmacological action of insulin. Indian Journal of Medical Research 2009;130:166-169.
- Q & A: How Long Can NPH Insulin be Used Once a Vial is Started? http://endocrinevet.blogspot.com/2012/02/q-how-long-can-nph-insulin-be-used-once.html