I recently received the following question:
How long can you keep bottles of insulin in the fridge? I have insulin from two years ago and wanted to see how long it's safe to use.
People with diabetes who are on insulin may at least once in their lives face this issue.
Insulin storage requirements are listed on the label, and are given for room temperature and for refrigeration. Look for a section with words like the following:
16.HOW SUPPLIED/STORAGE AND HANDLING
There may be more information written like:
Vials must be discarded 28 days after being opened. If refrigeration is not possible, the open vial can be kept unrefrigerated for up to 28 days away from direct heat and light.
Unopened vials, cartridge systems, and the device should be stored in a refrigerator, 36°F – 46°F (2°C – 8°C). Discard after the expiration date" [which is on the vial itself]
What happens after the expiry date? Probably not much. Most likely, the insulin will very gradually lose its potency, so each milliliter of insulin will have a bit less effect on lowering BG levels. That's usually not a problem, if you are checking BG regularly, and adjusting insulin doses. Until you start a new vial -- switching from an old impotent vial to a new standard-potency vial may cause you to crash into hypoglycemia if you don't decrease the dose with the very first dose you draw up from the new vial.
Another thought about old insulin: It's possible that as time goes by, the insulin might crystallize. This was a definite problem in years gone by, if insulin was stored out-of-spec, and could occur if insulin is frozen or overheated. Crystals of insulin in a vial might appear like a layer of frost on the inside of the glass, or white clumps, or a solid white layer at the bottom of the vial. Don't use vials that show any of these effects. (And you probably can ask the manufacturer for a replacement vial if you contact them and inform them of what happened.)
For more information on insulin: