Pet diabetes and the role of insulin pens

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Diabetes mellitus is a common endocrinopathy in both dogs and cats. Though mechanistically different, the disease in both species typically requires the administration of insulin to the pet. Historically, the administration of insulin to pets has typically been via an insulin syringe. Insulin pens were developed for use in people with diabetes and have virtually replaced the use of the syringe due to their multiple advantages. Their use in companion animals has become more popular, and an insulin pen specifically designed for dogs and cats is available as an option for pet owners who prefer an alternative to syringes. As the incidence of diabetes increases in our patients1, it is important that we provide our clients and patients with the best treatment options available. Adding Insulin Pens to that arsenal will assure that all options are being provided and may even help convince reluctant pet owners to treat their diabetic pet.

What is an insulin pen?

Insulin pens are simply insulin delivery devices that look like oversized ink pens. They come as either pre-filled (which are typically disposed of after single use) or refillable (where the pen is retained, and the cartridge is replaced). They have a dial at the bottom that allows the user to select a dose, and a trigger button to release the dose, which may be on the bottom or the side, depending on the model. It should be noted that human Insulin Pens use U100 insulin whereas the veterinary insulin pen uses U40 insulin. Insulin Pens require specific Pen needles to be attached prior to administration. Prior to use, Insulin Pens require a priming process to expel air bubbles trapped in the cartridge. After injection, it is recommended to keep the needle under the skin for 5-10 seconds. Since this is unfamiliar technology, it is imperative that veterinary staff familiarize themselves with insulin pens and their use as well as allocating a reasonable amount of time to familiarize the pet owners as well.

What are the advantages of an insulin pen over a syringe?

 With insulin syringe use, there is a known propensity for up to 25% more insulin to be drawn up per dose especially for smaller insulin doses.2,3 In contrast, Insulin Pens are known to be both accurate (giving the expected dose) and precise (giving a similar dose to the one previously given). For our small patients (i.e. those needing dose adjustments in ½ IU increments) this is particularly important. Insulin pen needles are also known to cause less injection site pain than those of insulin syringes,4 and provide pet owners with the added convenience of being able to carry their pet’s insulin together with its administration device simultaneously. People who use insulin pens find them to be overall more convenient and easier to use than insulin syringes, ultimately decreasing the stress associated with insulin administration.5

When should I consider an insulin pen?6

  1. Patients that experience pain with needle injections.
  2. Owners who are afraid of needles/injections.
  3. Patients that require ½ IU incremental dosage adjustments or seem sensitive to dosage changes
  4. Patients whose owners have difficulty drawing up insulin via a syringe, either due to dexterity or visual challenges.
  1. Households where multiple people administer insulin to the pets. 2

Typical steps of using an insulin pen6

  1. Attach a new Pen needle.
  2. Mix insulin per manufacturer’s instructions.
  3. Prime the insulin cartridge by dialing up 1 IU intervals until insulin is expelled.
  4. Dial up desired dose and administer.
  5. Hold the pen in place for the manufacturer’s recommended time.
  6. Remove needle from Pen and dispose of properly.
  7. Store Pen with no needle at the manufacturer’s recommended temperature.
  8. Dispose of Pen/vial after the manufacturer’s recommended days in use.

Common problems 6

  1. A drop of insulin at the tip of the needle after injection: This may be normal but may also be a sign of improper priming.
  1. Dose selector does not return to zero position: This may be a sign that either the release button wasn’t fully pressed, or the Pen is held in a manner that inhibits its ability to move.
  1. Air bubbles: Typically resolved with priming.

Insulin pens provide an alternative, accurate and precise delivery method for insulin. For the right animal and owner, Insulin Pens can be the difference that leads to treatment success.

by Nyssa Reine-Salz, DVM, DACVIM, Internal Medicine Consultant

Companion Animal Technical Services, Merck Animal Health



  1. Banfield Study 2016; Data covers 2005-2015 dogs and cats
  2. Burgard S, et al. Comparative laboratory evaluation of dose delivery using a veterinary Insulin Pen. BSAVA World Congress Proceedings, April 2012.
  3. Casella SJ, et al. Accuracy and Precision of Low-Dose Insulin Administration. Pediatrics 1993;91;1155.
  1. What Can We Learn from Patient-Reported Outcomes of Insulin Pen Devices? Anderson BJ et al. J Diabetes Sci Technol 2011;5(6):1563-1571
  2. Ripudaman S, et al. A Comparison of Insulin Pen Devices and Disposable Plastic Syringes –Simplicity, Safety, Convenience and Cost Differences. European Endocrinology. 2018;14(1):47–51
  3. Thompson A, et al. Update on insulin treatment for dogs and cats: insulin dosing pens and more. Vet Med (Auckl) 15 April 2015 Volume 2015;6: 129—142.

Photo credit: © iStock/kobzev3179

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