Managing of feline diabetes (Proceedings)

In 2005 Eli Lily announced the discontinuation of the majority of animal derived source insulins in addition to the lente and ultralente lines of product. This changed the landscape of veterinary diabetic management. Ultimately, the best insulin for your patient may be the one you are most familiar with; however, general guidelines will help choose the insulin that will give you the best success with your patients. Selection of insulin type is not the sole decision in management of the diabetic feline. Nutrition must be addressed and in some cases, the use of oral hypoglycemics may be considered in the cat, but not the dog. Finally, providing your client and staff with proper monitoring choices is essential for successful management.

Insulin can be classified according to source as well as duration of action. Beef and pork were traditional species used for insulin. Dogs, pigs, and humans have similar amino acid sequences of insulin, differing by only one amino acid between human and dogs and pigs, which are identical. In contrast, the protein sequence of feline insulin is much more different than the human sequence and differs by four amino acids but is quite similar to insulin derived from cows, differing by only one amino acid. Clinically, the most significant aspect of these differences is the development of antibodies in the dog. The use of beef source insulin is not recommended as in published studies the development of insulin antibodies in dogs administered a beef/pork insulin combination ranged between 40 and 65%. Despite the source of insulin used, the few studies examining this phenomenon do not suggest that insulin antibodies develop to a significant degree in the cat.

Currently, human recombinant is the most commonly available source of insulin, however, some specialized veterinary products are available. Vetsulin (Caninsulin outside the US, Intervet/Schering-Plough Animal Health) is a porcine lente insulin that is a mixture of 30% amorphous zinc insulin and 70% crystalline zinc insulin. In the past, a veterinary specific PZI (PZIVet) consisting of a 90% beef and 10% pork mixture was marketed by IDEXX Pharmaceuticals but has since been discontinued, with limited supplies remaining with distributors. Boehringer Ingelheim Vetmedica has recently announced a similar product based on recombinant human sequences but published studies and details are yet to be available. Duration of insulin varies within patients but can be somewhat reliably predicted. The chart below compares commonly available insulin potencies and a rough guide to durations of action.

Two insulin types, lispro and aspart, are insulin analogues and are very short acting. However, no data regarding their use in veterinary medicine is available at this time. Most recently, the use of Detemir in cats has been reported in a single abstract presented at ACVIM in June 2009 (Roomp, 2009) with similar remission rates as glargine. No further data is available at this time.

While both glargine and PZI have been reported as once daily insulins in the cat, most often, twice daily administration is more appropriate. Remission has been seen in newly diagnosed diabetic cats with the use of twice daily dosing of glargine and a low carbohydrate, high protein diet. Historically, kitten food has been used as the choice diet for overweight, insulin resistant type diabetic cats. However, several commercial diets incorporating a higher protein, lower carbohydrate, but calorie controlled formula have been introduced. In order to achieve remission and long term control, use of these diets is ideal if not required. Clearly, if cats will not eat these diets, the original food is acceptable; however, remission and control will be more difficult.

Glucose monitoring has changed over the past years as well. Glucose curves are still used to determine duration of action and onset, however, the use of fructosamine has added to our monitoring capacity. Fructosamine levels have reported to be reflective of the average glucose over the past two to three weeks, however, a recent publication using experimentally induced hyperglycemia in cats suggests a duration more likely associated with levels over the past 7-10 days (Link, 2008). However, these were experimentally induced hyperglycemic states; therefore, further studies in cats with naturally occurring disease are needed to truly define the duration of time fructosamine reflects.

At home glucose monitoring can be achieved via several different methods. Urine glucose strips are used to monitor for hypoglycemic events and should not be used by owners to adjust insulin doses upward. Most often these are used during the start of a new therapy or increased dose. Trace to 1+ urine glucoses are perfectly appropriate in diabetic animals, however, consistent negative urine glucoses suggest overdosage of insulin. Venous blood glucoses using peripheral ear vein samples and an at home glucometer can be a tremendous asset in monitoring feline patients. At home blood glucose curves remove some of the stress associated with curves and allow for longer curves for those practitioners who do not have overnight care available in the clinic. However, glucometers must be calibrated initially to a reliable glucose measurement and the owner should not be allowed to change doses without consulting with the veterinarian. Finally, continuous glucose monitoring using disposable implantable interstitial fluid glucose probes allows monitoring of glucose continuously throughout the day as long as the cat will tolerate the pack necessary for the unit. While all of this data will aid the practitioner in managing the diabetic feline, the MOST important monitoring parameter to be used is clinical signs: PU/PD? Appetite? Energy level? Body weight? Without those answers, no adjustments should be made.