Insulin is a hormone that regulates blood glucose (sugar) levels. For individuals with diabetes, insulin therapy is essential to manage these levels and prevent complications. The effectiveness of this medication relies significantly on proper handling and storage. Maintaining insulin’s integrity is important to ensure it delivers its intended therapeutic effect and supports patient well-being.
Factors Influencing Insulin Stability
Insulin is susceptible to degradation from various environmental factors, which can reduce its effectiveness. Exposure to extreme temperatures, both excessive heat and freezing, can cause insulin molecules to break down. For instance, temperatures above 86°F (30°C) can increase degradation, while freezing can lead to irreversible damage. Light exposure, particularly direct sunlight, also contributes to the breakdown of insulin.
Physical agitation, such as vigorous shaking, can similarly destabilize insulin. These changes reduce the bioavailability of the insulin, meaning less active medication is available to the body. Specific handling guidelines are necessary to maintain insulin’s potency.
Insulin Expiration Guidelines
Once opened or punctured, insulin begins a new countdown for its effectiveness, regardless of the expiration date on the unopened package. This “in-use” expiration period varies by insulin type and formulation. These timelines start from the first use or puncture, not from the date of purchase.
For insulin vials, a common timeframe for use after opening is 28 days. Many rapid-acting insulins like Humalog, Novolog, and Apidra vials are stable for 28 days once punctured. Similarly, long-acting insulins such as Lantus vials also typically remain potent for 28 days after initial use.
However, some variations exist. For example, Levemir vials can last up to 42 days, while Tresiba vials may be used for up to 56 days. Humulin R vials generally have a 31-day in-use period, and Novolin R vials can extend to 42 days.
Insulin pens, both pre-filled and reusable cartridges, also have specific post-opening expiry dates, often aligning with or differing slightly from vials. Most rapid-acting pens like Humalog, Novolog, and Apidra are good for 28 days once opened. Long-acting pens such as Lantus (glargine U-100) and Basaglar are typically stable for 28 days.
However, Levemir FlexTouch pens can last for 42 days, and Toujeo SoloStar (glargine U-300) and Tresiba FlexTouch pens extend to 56 days. Some mixed insulins, like Humalog Mix 50/50 and 75/25 pens, have shorter in-use periods, around 10 days, while Novolog Mix 70/30 pens may last 14 days. Always refer to the specific manufacturer’s instructions for the precise expiration guidelines for each product, as variations are common.
For insulin used in pump reservoirs, the stability period is generally shorter due to continuous exposure to body temperature and potential for aggregation. Insulin in an infusion set or reservoir is often recommended to be discarded after 3 to 7 days, depending on the pump system and insulin used. This shorter duration accounts for the constant physical movement and warmth the insulin experiences within the pump system.
Identifying Compromised Insulin
Even if within its stated post-opening timeframe, insulin can become compromised if not stored or handled correctly. Visual inspection is an important way to assess its integrity. Clear insulins, such as regular, rapid-acting, and long-acting types, should remain clear and colorless. If these insulins appear cloudy, discolored, or contain any particles, clumps, or “snowflakes,” they should not be used.
Some insulins, like NPH (intermediate-acting) and pre-mixed insulins, are naturally cloudy and appear milky white. This cloudiness is normal. However, even these cloudy insulins should be discarded if they appear unusually clumpy, granular, or have solid particles that do not disperse evenly after gentle rolling. Any change in texture, such as a gritty feel, or an unusual smell indicates spoilage. If any of these signs are present, the insulin’s potency is likely reduced or lost, and it should be discarded.
Risks of Using Expired Insulin
Using insulin that has expired or been compromised carries health risks due to its reduced or complete loss of potency. When insulin is less effective, it cannot adequately lower blood glucose levels, leading to hyperglycemia, or high blood sugar. Persistent hyperglycemia can cause symptoms like increased thirst, frequent urination, and fatigue. For individuals with type 1 diabetes, unmanaged hyperglycemia can quickly progress to diabetic ketoacidosis (DKA), a serious and potentially life-threatening condition. DKA occurs when the body produces harmful ketones due to insufficient insulin.
Proper Insulin Storage and Disposal
Proper storage is essential to maintain insulin’s stability and extend its usable life. Unopened insulin, whether vials or pens, should always be stored in a refrigerator, typically between 36°F and 46°F (2°C and 8°C), until its labeled expiration date. Once opened and in use, most insulin products can be kept at room temperature, generally between 59°F and 86°F (15°C and 30°C). It is important to avoid freezing insulin or exposing it to direct sunlight or extreme heat.
For disposal of used insulin supplies, safety is important. Needles and syringes, known as sharps, should always be placed in an FDA-cleared sharps container immediately after use. If a commercial container is unavailable, a heavy-duty plastic container with a tight-fitting lid can serve as an alternative. Always consult local regulations for disposal guidelines for sharps and empty insulin containers.