Diabetes mellitus is a common endocrinopathy in feline practice. Cats with diabetes can be challenging to monitor and treat
because of the complex pathophysiology of the disease and cats' propensity for stress-related hyperglycemia. In addition,
the small size of feline patients makes insulin dosing more difficult. This article will review reasons for poor diabetic
regulation and outline a logical approach to the difficult-to-treat diabetic cat.
APPROACH TO THE PROBLEM DIABETIC CAT
In general, problems with diabetic control can be categorized as insulin-related, client-related, or patient-related. Although
patient-related problems are more common, it is wise to carefully exclude insulin- and client-related issues first, since
these are often easily identified and addressed. When insulin- and client-related issues have been ruled out, we then start
to look for patient-related problems.
Sudden loss of regulation in a previously well-controlled diabetic may be due to problems with the insulin itself. Even if
you have no specific reason to suspect a loss of biologic activity with the insulin, it is always wise to just discard the
present bottle and start a new one. Insulin is a peptide and, therefore, can be damaged by exposure to heat or extreme cold.
With some insulin types, agitation during shipping can also damage the molecule and alter its biologic effects. Another consideration
is bacterial contamination; this can occur quickly and result in degradation of the insulin molecules and loss of potency.
And lastly, dilution of the insulin can cause problems as the product may behave differently or become unstable. Before conducting
an exhaustive and expensive search to identify patient-related problems leading to insulin resistance, it may be worthwhile
to replace an older insulin vial with a new, undiluted one.
Most feline diabetics are treated with protamine zinc insulin (PZI), insulin glargine (Lantus—Sanofi-aventis), or a pork Lente
product (Vetsulin—Intervet/Schering-Plough Animal Health). Various compounding pharmacies market beef PZI products, but these
facilities are not FDA-regulated, and quality control may be a concern. In November 2009, the FDA approved a U40 human-recombinant
PZI (ProZinc—Boehringer Ingelheim) for use in cats. It is advisable to switch to this product if a cat receiving compounded
PZI becomes unregulated. Dose equivalency may be questionable, so it is prudent to start again with a conservative dose (0.25
The only insulin glargine product currently available is a U100 formulation (i.e. each milliliter contains 100 units). Dosing small cats with a U100 product can be difficult, and practitioners may be tempted
to dilute the insulin. However, the slow absorption of insulin glargine depends partly on its acidic pH. Dilution will markedly
affect the pharmacokinetics and should never be considered. If anything has been added to the bottle, discard it and start
again with an undiluted product.
Probably the biggest client-related problem reflects the technical difficulties of drawing up small doses of insulin. It is
helpful to use a 0.3-ml syringe with a U100 insulin. Also, a syringe magnifier may provide some assistance. However, careful
instruction about elimination of air bubbles and other methods to ensure accuracy is essential.
It is prudent to watch the client draw up and administer an insulin dose. Watch carefully for problems with the injection
technique, such as intradermal injection or a through-and-through injection. Some owners tend to withdraw the syringe while
injecting, so the insulin actually ends up lost in the pet's coat. Checking for moisture on the fur after the injection can
be helpful, as can experimenting with a different needle size or length. Practicing with 0.9% saline injections is a safe
and effective way to train clients and increase their confidence. Shaving a small patch of hair may let clients visualize
the needle penetrating the skin and improve accuracy. You should not need to shave multiple sites unless a client is having
difficulty giving injections.