Insulin is a hormone produced by the pancreas that helps the body’s cells absorb glucose for energy. For individuals with diabetes, manufactured insulin is administered to manage blood sugar levels when the body doesn’t produce or use enough insulin. Some people with diabetes require more than one type of insulin for stable blood glucose control. To simplify administration, different insulin types can sometimes be combined into a single syringe. This practice requires specific knowledge and direct guidance from a healthcare professional.
Understanding Insulin Types and Mixability
Insulin formulations are categorized based on how quickly they start working, when they reach their peak effect, and how long their effects last in the body. This is known as their action profile. Different types meet varying blood sugar management needs.
Rapid-acting insulin analogs, such as insulin lispro (e.g., Humalog), insulin aspart (e.g., NovoLog), and insulin glulisine (e.g., Apidra), begin working within 5 to 15 minutes, peak in 1 to 2 hours, and last for 4 to 6 hours. These insulins are clear in appearance.
Short-acting insulin, also known as regular insulin (e.g., Humulin R, Novolin R), has a slightly slower onset, starting to work in about 30 minutes, peaking in 2 to 3 hours, and lasting for 5 to 8 hours. This type of insulin is also a clear solution.
Intermediate-acting insulin, NPH insulin (e.g., Humulin N, Novolin N), has an onset of 2 to 4 hours, peaks in 4 to 12 hours, and lasts for 12 to 18 hours. NPH insulin is cloudy due to added substances that slow its absorption.
Long-acting insulin analogs, including insulin glargine (e.g., Lantus, Basaglar, Toujeo), insulin detemir (e.g., Levemir), and insulin degludec (e.g., Tresiba), provide a sustained, “peakless” effect over a longer duration. Their onset is 1.5 to 2 hours, and they can last from 12 to 24 hours, with insulin degludec lasting up to 36 hours. These long-acting insulins are clear solutions. Pre-mixed insulins are already formulated combinations and should not be mixed with other insulins.
NPH insulin is the primary type that can be combined with other insulins in the same syringe. NPH insulin can be mixed with rapid-acting insulins like insulin lispro (Humalog) or insulin aspart (NovoLog), as well as with short-acting (regular) insulin. This combination allows for both immediate and prolonged blood sugar control with a single injection. If mixing rapid-acting insulins with NPH, they should be from the same manufacturer.
In contrast, long-acting insulins such as insulin glargine, insulin detemir, and insulin degludec should never be mixed with any other insulin. Mixing long-acting insulins can disrupt their specific chemical properties, leading to unpredictable effects on blood sugar levels. Pre-mixed insulins are also designed for standalone use and should not be combined with other insulin types.
How to Properly Mix Insulin
Mixing compatible insulins in the same syringe requires a specific procedure for accurate dosing and to maintain insulin integrity.
First, wash your hands with soap and water. Gather supplies: the two insulin vials, a new sterile insulin syringe, and alcohol wipes.
Before drawing any insulin, gently roll the cloudy NPH insulin vial between your palms until it appears uniformly milky white. Avoid vigorous shaking, as this can introduce air bubbles. Clean the rubber tops of both insulin vials with alcohol wipes.
The “clear before cloudy” rule guides the order of drawing insulin. First, draw air into the syringe equal to the NPH insulin dose, then inject this air into the NPH vial. Next, draw air equal to the clear insulin dose and inject it into the clear insulin vial.
Invert the clear insulin vial and draw the prescribed dose into the syringe. Check for air bubbles and remove them.
Then, insert the needle into the cloudy NPH insulin vial, invert it, and draw the exact NPH dose. Drawing clear insulin first prevents NPH contamination of the clear insulin vial, which could alter its action profile. Inject the mixed insulin immediately after preparation. If you overdraw, discard the syringe and start over with a new one.
Key Safety Guidelines for Insulin Mixing
Insulin mixing should only be done under the direct instruction and supervision of a healthcare provider. This article provides general information, but individualized medical advice is always necessary for safe diabetes management.
A key safety rule is that long-acting insulins, such as insulin glargine (Lantus), insulin detemir (Levemir), and insulin degludec (Tresiba), must never be mixed with any other insulin or diluted. Mixing them can disrupt their consistent release, leading to unpredictable blood glucose levels.
Always check the labels of all insulin vials to confirm the correct type and expiration date before use. Relying solely on appearance or label color can be misleading, as some clear insulins are long-acting and should not be mixed. If any insulin has particles, lumps, flakes, or discoloration, it should not be used.
Use a new, sterile syringe for each injection to prevent infection. Syringes are designed for single use; reusing them can introduce bacteria or affect needle sharpness.
Proper storage maintains insulin potency. Unopened insulin should be refrigerated between 36°F to 46°F (2°C to 8°C) until its expiration date. Opened vials or pens can be stored at room temperature, between 59°F and 86°F (15°C to 30°C), for up to 28 days. Never freeze insulin or expose it to extreme heat or direct sunlight, as this degrades its effectiveness.
Consistent monitoring of blood glucose levels is important, especially when starting a new insulin regimen or making changes, including mixing insulins. This helps assess effectiveness and allows for timely adjustments. It is also important to be aware of hypoglycemia (low blood sugar) symptoms, which can occur with insulin use. Symptoms include shakiness, sweating, dizziness, confusion, hunger, or a fast heartbeat. Knowing these signs and how to respond, usually by consuming a quick source of sugar, is important for insulin safety.