Insulin is a protein hormone produced by the pancreas, playing a direct role in regulating blood glucose levels. For individuals with diabetes, insulin administration is necessary to manage these levels and prevent complications. As a protein, insulin is susceptible to degradation by various environmental factors, which can diminish its effectiveness over time.
Factors Influencing Insulin Potency
Temperature impacts insulin’s stability. Unopened insulin vials or pens should be stored in a refrigerator, between 36°F and 46°F (2°C and 8°C), to maintain potency until the manufacturer’s expiration date. Once opened or in use, most insulin products can be stored at room temperature, between 59°F and 86°F (15°C and 30°C), for up to 28 days. Newer research suggests some unopened human insulin types might retain potency for up to six months at temperatures up to 77°F (25°C), which could be helpful in situations without reliable refrigeration.
Insulin should not be frozen, as it loses effectiveness. Conversely, exposure to excessive heat, such as leaving insulin in a hot car or direct sunlight, also degrades the protein and reduces its ability to lower blood sugar. If insulin is exposed to temperatures above 98.6°F (37°C), it should be discarded.
Direct sunlight or strong artificial light can degrade insulin, so keep vials and pens protected from light exposure. Physical agitation, like vigorous shaking, can damage the insulin molecule, especially for certain formulations, reducing potency.
The manufacturer’s expiration date applies to unopened, refrigerated insulin. Once opened, however, an “in-use” expiration date, around 28 days for most types, takes precedence. Some insulin formulations have different in-use durations, ranging from 10 to 56 days, so consulting the specific product’s instructions is always recommended. Insulin diluted or removed from its original vial for pump use has a shorter lifespan, around two weeks.
Identifying Degraded Insulin
Visually inspecting insulin before use is a straightforward way to check for signs of degradation. Clear insulins, such as rapid-acting or long-acting types, should appear transparent and colorless. If these insulins show any cloudiness, clumps, or discoloration, they should not be used.
For cloudy insulins, like NPH, it is normal for them to appear uniformly cloudy. However, if you observe clumps, threads, or any unusual particles, even after gently rolling the vial or pen, the insulin is compromised. Frosting or crystals inside the vial or pen are also indicators that the insulin is degraded.
Beyond visual cues, an unexpected rise in blood sugar levels despite proper insulin dosing indicates ineffective insulin. If there is any doubt about the quality of insulin, it is safer to discard it and begin using a new, properly stored vial or pen.
Safe Handling and Disposal
Proper storage practices maintain insulin’s potency. Unopened insulin should be kept refrigerated until its expiration date. Once opened, store insulin at room temperature, away from direct heat and sunlight. Avoid exposing insulin to extreme temperatures, such as leaving it in a hot car or near a window.
When traveling, keep insulin in your carry-on bag to protect it from extreme temperatures that can occur in checked luggage. Insulin pens should never be stored with a needle attached.
Expired or degraded insulin, along with used needles and syringes, requires careful disposal to prevent injury or contamination. Used needles and syringes should be placed immediately into a puncture-resistant “sharps” container. These containers can be obtained from pharmacies or medical supply stores, or a sturdy plastic bottle with a secure cap can serve as a temporary alternative.
Do not dispose of loose needles, syringes, pens, or vials in household trash or recycling bins. Expired insulin vials or pens, and other unused diabetic supplies, should be disposed of according to local guidelines, which may include medication take-back programs offered by pharmacies or hazardous waste disposal centers. Never flush insulin or sharps down the toilet.