Insulin therapy plays a critical role in the management of diabetes in both dogs and cats. Insulin is available in various formulations, including vials, pens, and cartridges. Different types of insulins are supplied in different concentrations, such as U-40 (40 units/mL), U-100 (100 units/mL), and U-300 (300 units/mL).
Understanding Insulin Syringes
It is important to inform owners that insulin syringes are not interchangeable. A U-40 syringe must be used to administer U-40 insulin, and a U-100 syringe must be used to administer U-100 insulin. The 1-unit mark on both a U-40 and a U-100 syringe will deliver 1 unit of insulin, however, the volume delivered will be different. This is a key concept for owners to understand, especially when transitioning between insulin products.
A new needle (if using an insulin pen), or needle and syringe (if using an insulin vial), should be used for each dose to prevent potential contamination or transmission of infectious agents.
Storage of Insulin
Unopened insulin products should be stored in a refrigerator at 2°C to 8°C (36° F to 46°F), regardless of brand or type. An ice pack may be provided to clients when dispensing insulin to help maintain proper temperature during transportation. However, the insulin should not come into direct contact with the ice pack. If insulin is frozen, it should be discarded due to degradation, as recommended by manufacturers.
Once opened, human insulin products may be stored at room temperature or under refrigeration (check the relevant package insert), while veterinary insulins must remain refrigerated. Each insulin formulation has its own handling instructions, with some requiring gentle rolling before use, while others may require shaking.
In all cases, insulin should be protected from direct sunlight and excessive heat to prevent degradation. It is strongly advised not to leave insulin products in a vehicle.
Discarding Insulin
Most manufacturers recommend discarding opened insulin after 28 to 60 days. Using insulin beyond the recommended discard date is not advised. However, if an owner chooses to do so, they should keep the insulin stored appropriately and monitor for any signs of degradation, such as discoloration, particulates, and changes in consistency. They should be advised that signs of degradation may not be visible.
Using insulin beyond the recommended discard date may result in reduced effectiveness. If an animal presents with suboptimal glycemic control, check how long the owner has been using the current insulin supply. If it is longer than recommended or the insulin has been stored inappropriately, it is reasonable to consider replacing the product and continuing the current dose to see if glycemic control is achieved.
For detailed guidance on temperature requirements, shelf life, and stability of insulin products, consult the manufacturer’s package insert or contact a pharmacist.
References
- Behrend EN, Holford A, Lathan P, Rucinsky R, Schulman R. 2018 AAHA Diabetes Management Guidelines for Dogs and Cats. J Am Anim Hosp Assoc. 2018;54(1):1–21. doi:10.5326/JAAHA-MS-6822
- DailyMed. Vetsulin–porcine insulin zinc suspension. U.S. National Library of Medicine. Accessed June 11, 2025. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4472644f-edc1-4a4f-8506-888bd8ad895a
- Plumb DC. Insulin Aspart. In: Plumb’s Veterinary Drugs. Wiley-Blackwell; 2025. Accessed June 11, 2025. https://app.plumbs.com/drug/2BQupCm5DAqOlkZeCZPOay
- Plumb DC. Insulin Detemir. In: Plumb’s Veterinary Drugs. Wiley-Blackwell; 2025. Accessed June 11, 2025. https://app.plumbs.com/drug/72XVA0NW5iSDofBM5Wfbo8
- Plumb DC. Insulin Isophane (NPH). In: Plumb’s Veterinary Drugs. Wiley-Blackwell; 2025. Accessed June 11, 2025. https://app.plumbs.com/drug/3pxV85IY74qDjVfaZvgu2I
- Plumb DC. Insulin Lispro. In: Plumb’s Veterinary Drugs. Wiley-Blackwell; 2025. Accessed June 11, 2025. https://app.plumbs.com/drug/1sddfeBtfpuJ1fX6gP6jNf
- Plumb DC. Protamine Zinc Insulin (PZI). In: Plumb’s Veterinary Drugs. Wiley-Blackwell; 2025. Accessed June 11, 2025. https://app.plumbs.com/drug/6B3LOCFS2QE6iSj98rHSN1
- Plumb DC. Vetsulin. In: Plumb’s Veterinary Drugs. Wiley-Blackwell; 2025. Accessed June 11, 2025. https://app.plumbs.com/drug/2i0sgFiK8EF88ebZHlXVCK
By Sharon Huang, fourth-year pharmacy student at University of Illinois–Chicago
