Screen all cats over 6 years of age for hyperthyroidism by measuring a total thyroxine (T4) concentration. If the concentration is at the upper end of the normal range, early hyperthyroidism may be more readily identified
by measuring the free T4 concentration by equilibrium dialysis.3 Dogs with untreated diabetes may have low total T4 concentrations because of euthyroid sick syndrome. So evaluate a free T4 concentration and thyroid-stimulating hormone concentration before starting thyroid supplementation.
Of course the mainstay of therapy for every diabetic dog and most diabetic cats is insulin. But which type of insulin should
you use, what's the best way to initiate therapy, and how do you ensure that you continue to administer an appropriate dose?
What's the most appropriate diet for a diabetic dog or cat? These considerations are essential in achieving and maintaining
good glycemic control.
Table 1: A Comparison of Insulin Products Commonly Used in Cats and Dogs
Choosing an insulin
Insulins are categorized by species of origin (porcine, bovine, recombinant human) and duration of action (short, intermediate,
long) (Table 1). When selecting a product for at-home use, it is important to consider species (feline insulin is most similar to bovine,
whereas canine insulin is identical to porcine and similar to human). Feeding habits are also important: Dogs tend to eat
defined meals, whereas cats are more likely to graze. The owner's schedule may also be a factor, and once-daily vs. twice-daily
dosing may improve overall compliance (see boxed text "What clients need to know").
What clients need to know
The cost of insulin varies. The veterinary-licensed products are generally more expensive than human ones and require particular
syringes (designed for U-40 insulin) that are not available at human pharmacies.
The following is intended as a general description of insulin products commonly used in cats and dogs. It does not cover every
formulation presently available, and readers are urged to carefully research any unfamiliar type before starting therapy.
Doses are provided here as a guide and must always be tailored to a patient's specific requirements.
Regular insulin. Regular insulin is a human recombinant type available in a U-100 concentration (e.g. Humulin R—Eli Lilly, Novolin R—Novo Nordisk). Regular insulin is highly potent and is generally reserved for in-hospital
use in ketoacidotic animals. It is the only insulin that can be administered intravenously. Careful monitoring is necessary
to prevent a precipitous drop in serum glucose concentrations, and it is not an appropriate choice for at-home therapy.
Vetsulin. This Lente insulin from Intervet, known as Caninsulin outside the United States, is of porcine origin and comes in a U-40 concentration. It is an aqueous zinc suspension of amorphous
and crystalline insulin, which produces two peaks of activity—one soon after administration and the second several hours later.4