Insulin is a life-sustaining medication that helps regulate blood sugar in people with diabetes. Its effectiveness, known as potency, is highly dependent on proper handling and storage once the sterile seal is broken, or the medication is “opened”. Because insulin is a protein, it is sensitive to environmental factors and can break down over time, reducing its ability to lower blood glucose. Using degraded insulin is dangerous, as it can lead to uncontrolled high blood sugar levels and serious health complications.
The Standard 28-Day Rule
The standard guideline for most insulin products is that they must be discarded 28 days after the first use, even if liquid remains. This rule applies to common rapid-acting, short-acting, and long-acting insulins in vials, pens, or cartridges. The term “opened” or “in-use” refers to the moment the medication is first punctured with a needle or the first dose is administered.
The 28-day limit is based on the risk of contamination once the vial or pen stopper has been punctured, not solely on a loss of potency. Regulatory standards require that insulin retain at least 95% of its potency until the labeled expiration date, but manufacturers cannot guarantee sterility or full strength beyond 28 days under typical use conditions. This time frame assumes the insulin has been kept at the required room temperature, which helps maintain the protein structure.
Exceptions to the Standard Duration
While the 28-day rule covers most insulin products, some specific formulations and delivery methods have different recommended durations for in-use stability. Certain long-acting insulin analogues are engineered to maintain their stability for a longer period at room temperature. For instance, insulin detemir (Levemir) is stable for up to 42 days after opening.
Insulin degludec (Tresiba) offers an even longer in-use lifespan, often lasting up to 56 days, or eight weeks, once it has been opened. These extended durations are specific to the unique chemical structure and formulation of these insulins. Conversely, some delivery systems require a much shorter duration, such as insulin pump reservoirs and infusion sets, which typically hold insulin for only two to three days before the insulin must be discarded and the set changed.
Temperature and Handling Requirements
The durations mentioned for opened insulin are only valid if the medication is stored correctly within a specific temperature range. Once opened, most insulin should be stored at “room temperature,” defined as being between 59°F and 86°F (15°C and 30°C). This range is necessary because cold insulin can cause discomfort at the injection site, and temperature fluctuations compromise stability.
Unopened insulin must be refrigerated, between 36°F and 46°F (2°C and 8°C), to ensure maximum shelf life until the printed expiration date. Never freeze insulin, as this permanently destroys the protein structure and renders the medication ineffective. Opened insulin should be protected from direct heat (such as being left in a car or near a heat vent) and direct sunlight, both of which cause rapid degradation. Excessive physical agitation, such as vigorous shaking, can also compromise the insulin’s structure, which is why cloudy insulins should only be gently rolled before use.
Visual Signs of Insulin Degradation
Beyond adhering to time and temperature rules, visually inspect insulin before every use. Most modern insulins, including rapid-acting and long-acting types, are clear and colorless. Clear insulin that has degraded will show changes such as cloudiness, discoloration (like a yellowish tint), or the presence of solid particles, clumps, or thread-like strands.
Other insulins, such as intermediate-acting NPH insulin, are intentionally cloudy or milky in appearance due to added components that slow their absorption. If a cloudy insulin has spoiled, it may show clumping, a chalky white sediment sticking to the bottom or sides of the vial, or a frosted interior. Any insulin, whether clear or cloudy, that shows signs of degradation, such as crystallization or frost, must be immediately discarded.