Vetsulin is FDA-approved for use in dogs only. It can be used in cats, but insulin resistance secondary to anti-insulin antibodies
is a theoretical concern in this species. Some dogs may be adequately controlled with once-daily administration, but most
dogs require twice-daily dosing.5 I recommend a conservative starting dose of 0.5 U/kg, to minimize the risk of hypoglycemia. Doses should be adjusted based
on serial glucose measurements: increase by 10% to 15% in a persistently hyperglycemic patient (glucose > 250 mg/dl), and
decrease by 25% if hypoglycemia (glucose < 70 mg/dl) is noted.
NPH insulin. This form of insulin is a human recombinant type and is available in a U-100 concentration (e.g. Humulin N—Eli Lilly, Novolin N—Novo Nordisk). NPH is an intermediate-duration insulin, with modest potency. It can be used
in both cats and dogs and is an economical option in large dogs (when compared with Vetsulin). Twice-daily dosing is usually
necessary, and a starting dose of 0.5 U/kg is generally appropriate.6,7 As with Vetsulin, dosages should be adjusted based on serial glucose measurements: increase by 10% to 15% in a persistently
hyperglycemic patient (glucose > 250 mg/dl), and decrease by at least 25% if hypoglycemia (glucose < 70 mg/dl) is noted.
Protamine zinc insulin. Protamine zinc insulin (PZI) is 90% bovine origin and 10% porcine origin and is available in a U-40 concentration that is
FDA-approved for use in cats (PZI Vet—Idexx). It is a long-acting insulin and is an appropriate choice for diabetic cats.
Some cats achieve acceptable glycemic control with once-daily dosing, but twice-daily dosing is more common. The recommended
starting dose is 1 U/cat (0.22 to 0.6 U/kg). The dose can be increased in increments of 0.5 U if necessary. PZI is not suitable
in dogs because its onset and duration of effect are unpredictable and there is a risk of anti-insulin antibody formation.8
Glargine. Glargine, a human recombinant type, is a new form of insulin that is available in a U-100 concentration (Lantus—Sanofi Aventis).
It is a novel engineered insulin with an ultra-long duration of activity. It can take a few days to achieve its maximal effect,
and overdose can result in up to 72 hours of hypoglycemia. It is well-suited to cats, as the prolonged effect matches their
tendency to eat small, frequent meals. Many cats quickly achieve glycemic control, generally on a twice-daily dosing schedule.
The recommended starting dose is 0.5 U/kg of ideal body weight for cats with glucose concentrations > 360 mg/dl and 0.25 U/kg
of ideal body weight for cats with glucose concentrations between 200 and 360 mg/dl (Figure 1).2
Figure 1: Protocol for initiating glargine therapy in nonketotic diabetic cats
A surprisingly large number of newly diagnosed diabetic cats receiving glargine go into remission, most likely because of
the reversal of glucose toxicity,9 a condition in which persistent hyperglycemia inhibits the release of insulin from the pancreatic beta cells. If the glucose
concentrations are quickly normalized, the beta cells regain function, and the diabetes may resolve.
This insulin cannot be diluted, as its effect is pH-dependent. Dosing accuracy is improved if 0.3-ml 100-U syringes are used.
It is available in 10-ml vials and 3-ml cartridges; for cost reasons, some clients prefer to purchase the cartridges and have
the insulin decanted by a pharmacist into an appropriate container.