CVC Highlight: Insulin therapy for diabetes mellitus in dogs and cats: Ensuring your chances of success


CVC Highlight: Insulin therapy for diabetes mellitus in dogs and cats: Ensuring your chances of success

Picking the right insulin product, initiating and maintaining appropriate dosing, and performing regular monitoring are key.

J. Catharine Scott-Moncrieff
The variety of insulins to treat diabetes mellitus in veterinary patients is ever-changing. Make sure you're aware of all your options to ensure your patients receive the best treatment.


Following is a practical list (FDA-approved manufacturer's labels may be different) of options for insulin therapy. Veterinary-formulated insulin products (ProZinc—Boehringer Ingelheim Vetmedica; Vetsulin—Intervet/Schering-Plough Animal Health; Vetsulin is not currently available) are 40 U. Human-formulated insulin products are 100 U. It is imperative to match the product concentration to the appropriate syringe.

Short acting

Regular insulin—only used in sick diabetic patients

Moderate acting

NPH (isophane)

  • Onset 0.5 to three hours
  • Duration four to 10 hours (dogs), four to 12 hours (cats)


  • Amorphous insulin and crystallized insulin in zinc acetate buffer
  • Mixture of 30% semilente and 70% ultralente—can see two nadirs on blood glucose curve
  • Not currently available in the United States but may be back on the market soon.

Long acting

PZI—protamine zinc insulin

  • FDA approved for use in cats
  • Zinc and protamine (from trout semen) delay absorption
  • Onset one to four hours
  • Duration six to 28 hours (dogs), six to 24 hours (cats)


  • Forms microprecipitate at physiologic pH resulting in slow release over 24 hours
  • Cannot be mixed with anything
  • Time to nadir is long (11 to 16 hours)


  • Not a first-line choice
  • Long lasting (> 24 hours)
  • High risk for developing hypoglycemia
  • Dose range in dogs much lower than for other insulin products (0.07 to 0.23 U/kg)

Compounded insulin

The use of compounded insulin products is highly controversial. The perceived advantages of compounded insulin are lower cost, greater availability, a wide range of concentrations, and great customer service. That being said, there has been strong resistance to their use from veterinary specialists, who recommend against their use. (Anecdotally, these specialists have had problems with these products.)

An extensive study involving evaluation on a monthly basis of 12 compounded PZI insulin products and one from a manufacturer was conducted to help put an end to the speculation about these insulin products.1 Two vials from each batch were sent for testing every two months for four months (one blinded, one original). Many of the compounded products were found to have low potency, extremely high interlot variability, incorrect pH, free insulin in the supernatant, and incorrect zinc content. These findings support those specialists that recommend that compounded insulin should not be used.