Insulin is a hormone that plays an important role in managing blood sugar levels for individuals with diabetes. Its potency, crucial for effectiveness, can be compromised by improper handling and storage. Understanding correct storage is important for maintaining its therapeutic benefits. This article explores factors influencing insulin stability and provides guidelines for its storage, particularly when not refrigerated.
Factors Influencing Insulin Stability
Insulin, as a protein, is susceptible to degradation when exposed to certain environmental conditions. High temperatures can cause the insulin protein structure to break down, thereby reducing its ability to lower blood sugar. Exposure to temperatures exceeding 86°F (30°C) can lead to a loss of effectiveness. If insulin in a pump reservoir reaches above 98.6°F (37°C), it should be discarded.
Conversely, freezing temperatures also damage insulin molecules, rendering them ineffective even after thawing. Direct sunlight and strong indoor lights can contribute to insulin degradation, so it requires protection from light exposure. Furthermore, vigorous physical agitation, such as shaking, can physically damage the insulin molecule, causing it to aggregate and lose potency.
Unrefrigerated Insulin Guidelines
Unopened insulin vials, pens, and cartridges are generally recommended to be stored under refrigeration until their expiration date. Once removed from refrigeration or opened, most insulin products remain potent at room temperature for a specific period.
Most opened insulin vials, pre-filled pens, and cartridges can be kept at this room temperature for up to 28 days. However, specific formulations may have different durations. For instance, Isophane insulin might only be stable for 14 days at room temperature. Insulin Degludec (Tresiba) can often be used for up to 56 days once opened, whether stored at room temperature or refrigerated. Insulin Detemir (Levemir) typically maintains potency for 42 days after opening.
Certain other insulins also present variations in their unrefrigerated shelf life. Humulin R and Humulin N vials are stable for 31 days once opened. Some pre-mixed insulin pens, such as Humalog Mix 50/50 and 75/25, or Novolog Mix 70/30 FlexPen, have a shorter lifespan of 10 to 14 days after initial use.
Insulin transferred to an insulin pump from its original vial should be used within two weeks. Insulin within the pump’s reservoir or infusion set should be discarded after 72 hours, or sooner if exposed to temperatures above 98.6°F (37°C). Given these variations, always consult the specific product insert or packaging for accurate storage guidelines.
Recognizing Degraded Insulin
Identifying degraded insulin is important for effective diabetes management. Clear insulin, which should be colorless and transparent, may show signs of degradation if it appears cloudy, discolored, or contains particles, clumps, or stringy formations. The presence of crystal-like structures or a frosted appearance on the vial walls also indicates spoilage.
It is important to note that certain insulin types, such as NPH insulin (e.g., Humulin N and Novolin N), are naturally cloudy in appearance. However, unusual separation, clumping, or solid particles indicate degradation even for these types. Beyond visual cues, an unexplained rise in blood sugar levels despite consistent dosing can signal lost potency. If any of these signs are observed, or if there is doubt about the insulin’s integrity, it should be discarded and replaced.
Optimizing Insulin Storage
Proper storage practices help maintain insulin’s effectiveness and extend its shelf life. Unopened insulin should always be stored in a refrigerator, ideally between 36°F and 46°F (2°C and 8°C), until its labeled expiration date. Care should be taken to avoid placing it too close to the freezer compartment, as freezing renders insulin unusable.
Once an insulin vial or pen is opened, it can be kept at room temperature, generally between 59°F and 86°F (15°C and 30°C), for the duration specified by the manufacturer. It is important to protect all insulin, whether opened or unopened, from direct heat, freezing temperatures, and direct sunlight. Avoid leaving insulin in hot cars or near heat sources like stoves or radiators.
When traveling, carry insulin in hand luggage, protected in an insulated bag or cooling wallet to shield it from temperature extremes. Always check both the manufacturer’s expiration date on the package and the “in-use” expiration date, which begins once the insulin is opened. Degraded or expired insulin should be properly discarded.