Diabetes in Pets

Anecdotal evidence from the Feline Diabetes Message Board[1] shows that cats metabolize insulin noticeably faster than dogs or humans[2].

Intervet acknowledges the faster metabolism of cats in their Australian Caninsulin presentation at the link below[3], as does this study of the absorption of R/Neutral, NPH/Isophane. and PZI/Protamine Zinc insulins in cats[4][5].

From the Textbook of Veterinary Internal Medicine, Sixth Edition:[6]

"Diabetic cats are notoriously unpredictable in their response to exogenous (outside) insulin. No single type of insulin is routinely effective in maintaining control of glycemia, even with twice a day administration.
It is not possible to predict which type of insulin will work best in individual diabetic cats. The initial insulin of choice ultimately is based on the veterinarian's personal preference and experience."

Humans and dogs appear to metabolize insulin at about the same rate, but a frequently heard rule-of-thumb is that a cat will on average go through insulin* twice as fast as a human or a dog (individual cats will vary considerably)[7][8].

*Levemir may be an exception; as we become familiar with more new types of insulin, we may have to modify this rule to depend on insulin types and molecules too.

There are two current theories about why cats have less insulin duration than dogs or humans. One is due to absorption differences, with cats having only 45% bioavailability of injected insulin, while dogs have 65%[9]. The other contends that the short duration is due to counter-regulatory responses[10].

Therefore, most cats on insulins we're familiar with require injections twice a day (BID). Many, although certainly not all, veterinarians recommend BID insulin injections for cats. Some veterinarians may not recommend it at first, wanting to see how the cat responds to the insulin, or concerned that the caregiver may reject treating a cat that requires BID injections.

A glucose curve will show how a cat is utilizing the insulin over a 12 or 24 hour period. This can be done either at the veterinary clinic or by home-testing. A glucose curve will show when the insulin is peaking as well as how effective the insulin is in decreasing the blood glucose levels. Many cats seem to peak around the six hour mark and will have increasing blood sugar levels until their next dose of insulin.