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Photo of VetPen


VetPen from Merck Animal Health is the first and only veterinary insulin pen for use in the treatment of diabetes mellitus in dogs. To avoid dosing errors, VetPen must be used with 40 IU/mL, 2.7 mL Vetsulin cartridges.

When loading a new cartridge into VetPen, priming is necessary to remove air bubbles. And proper steps to prepare VetPen must be done before each injection. Click here for information on priming and preparing VetPen.

VetPen is available in 2 sizes: 8 IU VetPen with dosing increments of 0.5 IU and 16 IU VetPen with dosing increments of 1 IU. Vetsulin® (porcine insulin zinc suspension) (2.7 mL) cartridges are available in boxes of 10.

Advise pet owners not to reuse VetPen needles. After a single use, needles should be disposed of in approved sharps or biohazard containers.

U-40 versus U-100

Vetsulin is presented in a glass vial or cartridge at a concentration of 40 IU per mL of solution. To avoid dosing errors when administering Vetsulin to dogs, it is important to use a U-40 syringe or VetPen. USE OF A SYRINGE OTHER THAN A U-40 SYRINGE OR USE OF A 100 IU/mL CARTRIDGE WITH VETPEN WILL RESULT IN INCORRECT DOSING. VetPen was specifically designed for use with the Vetsulin cartridge concentration, formulation, and volume.

Some dog owners may attempt to replenish their syringe inventories and/or insulin supply from their local human pharmacies. Pharmacies carry U-100 (100 IU/mL) 1 mL and 50 IU/mL 0.5 mL syringes only. They do not stock 40 IU/mL 1 mL syringes, nor do they stock Vetsulin.

Using a U-100 syringe or human insulin pen with Vetsulin would result in a dog receiving two and a half times less insulin than required. Human insulin is formulated at a concentration of 100 IU/mL. If a client uses a U-40 syringe or VetPen with a 100 IU insulin preparation, they would be injecting two and a half times the amount of insulin necessary, which could result in fatal hypoglycemia.

Most pharmacists are not aware of Vetsulin, VetPen, or the U-40 syringes. As noted above, substituting a 100 IU/mL insulin product and/or a 100 IU/mL syringe could result in unsuccessful regulation, hypoglycemia, and even death.

As this potential situation can be fatal, it is strongly advised to educate clients to purchase both Vetsulin and the U-40 syringes from your veterinary clinic.


To help your clients prepare and administer Vetsulin to their dogs, there are resources available that guide them step-by-step through the process: