The mainstay of treatment for clinical DM in dogs and cats is insulin along with dietary modification. Goals include controlling BG below the renal threshold for as much of a 24 hr period as possible, which will improve clinical signs of DM, and avoiding clinically significant hypoglycemia.

Veterinarians use a variety of insulin products, but only two are presently approved by the FDA for use in dogs and cats. A porcine lente product (porcine zinc insulin suspension, Vetsulin) is approved for both species. Human recombinant protamine zinc insulin, or PZI (ProZinc) insulin, is also FDA approved for both cats (as of 2009) and dogs (as of 2019). It is considered by clinicians as a long-acting insulin. Because of limited controlled, comparative studies, most experts’ recommendations are based on a combination of clinical and anecdotal experience. The guidelines Task Force strives to make evidence-based recommendations when data are available. However, the ability to make specific recommendations based on differences and preferences between veterinary insulin products is limited. Members of the Task Force most commonly use porcine lente insulin (Vetsulin) in dogs and glargine (Lantus) in cats as their first choice, recognizing that other acceptable options used by many clinicians include Neutral Protamine Hagedorn (NPH; Humulin N, Novolin N) in dogs and PZI (ProZinc) in cats and dogs.

Although compounded insulin is available, its use is not recommended because of concerns about production methods, diluents, sterility, and insulin concentration consistency between lots. A study comparing commercially available insulin with its compounded counterparts showed that the manufactured insulin met all US Pharmacopeia requirements and only 1 of 12 compounders met US Pharmacopeia specifications at all time points. The variability between compounded insulins was also significant enough to have clinical consequences.¹¹ It is also not recommended to dilute insulin because dilution can produce unpredictable results, alter insulin efficacy, and result in bacterial contamination.^5,12