How long is it safe to use insulin once it is opened if it is stored in the refrigerator between uses?
Insulin pens or vials are considered “open” once the rubber stopper is punctured, and most brands are good for up to 28 days at room temperature or in the refrigerator. Refrigerating the open pen or vial does not make the pen stay “fresher”; it lasts the same amount of time whether the insulin is kept at room temperature or refrigerated. Once opened, Levemir pens and vials last a little longer than average (up to 42 days) and cloudy insulins pens, such as Novolog 70/30 and Humalog 75/25, last for a shorter time (up to 14 days). The package insert that comes with your insulin specifies how long it remains good once it is opened, or you can ask your local pharmacist. If the insulin is unopened, it must be kept refrigerated and is good until the expiration date on the vial or pen. The problem with using opened insulin beyond the guidelines listed on the package is that the insulin can lose its potency and not work as well to lower blood glucose levels.