Cat insulin is a frustrating topic. Cat diabetes has practically become an epidemic in the U.S. for many of the same reasons adult onset diabetes in people has risen dramatically - obesity and, in the case of cats, a diet that is too rich in carbohydrates.
However, unlike human diabetes who have many different types of insulin to chose from, the selection of insulin for cats has a history of being mainly unsatisfactory. That's because most insulin is made for people and when insulin is made specifically for animals, it has traditionally been directed at dogs.
When it comes to insulin, a cat's own natural insulin is most like beef insulin. Cats have also been successfully treated using beef-pork insulin because it is 10 percent pork and 90 percent beef. Unfortunately, I have seen such types of insulin that are most appropriate for cats come and go over the last 20 years. Just as a patient would get well-regulated on one type of insulin, it would be discontinued and we would have to start a different type. It has been a frustrating situation.
That's not to say that you cannot treat your diabetic cat successfully with insulin. Currently, due to a lack of animal-source insulins, most cats are started on human recombinant insulin.
Even in the field of human insulin where there have been dozens of different insulins available, so many have been discontinued - it's enough to make your head spin.
At the moment, there is an insulin developed just for cats. It's called PROZINC. Will it still be around a year from now? Who knows. Is it the best insulin? No. Does it work well in all cats? No. For that reason, your veterinarian will discuss with you the available types of insulin if your cat is diagnosed with diabetes and he will, no doubt, have his own preference.
ProZinc stands for Protamine Zinc Human Recombinant Insulin. It's labelled as being developed just for cats, however, right off the bat, you can see that it's not the most ideal for cats because it is not "cat" insulin, it's not pork or beef insulin, it is human recombinant insulin.
ProZinc is referred to as a long-acting insulin, which in the past, meant that you might have to inject your cat only once daily. However, ProZinc, in my experience, always requires an injection twice daily. The manufacturer even says that the duration of activity of the insulin is 10-14 hours, so it is pretty clear that two injections are necessary.
There are other insulins being prescribed for cats. Lantis is one that some cats seem to do well with and others not. But that's actually the case with most insulin. What is best for one cat may not be best for another.
There are compounding pharmacies that are still making bovine origin insulin which is closer to a cat's own insulin. Speak to your veterinarian about his/her experience in that regard. This type of insulin should produce superior results in cats due to the bovine type being closer to cat insulin than the human insulins are.
You will find many varying opinions. Some people, some vets swear by one type of insulin; others by another. Whatever insulin your cat is started on, if it is not working well, your kitty's insulin can be switched to a different type.
In my opinion, proper administration, proper dosing, and home-testing are as important as the type of insulin you use or perhaps more important. Likewise, your cat's diet is extremely important. Your diabetic cat should only eat canned, low carbohydrate food that in high in protein and has moderate fat.
There's a site where you can readily find the carbohydrate, protein and fat content of many canned foods. It's called Binky's Page and is a great source of information.
Cat insulin is the subject of the following letter from the owner of a cat with feline diabetes. It's certainly important that the feline insulin you use is effectively controlling your cat's diabetes and preventing such conditions as feline diabetic neuropathy.
My cat has had feline diabetes now for three months. Her sugar count is still really high. We have changed her cat insulin already three times. She is on 7 units of feline insulin twice a day. What do you think the problem could be?
There's a number of problems I see just from your question. I can't imagine changing the cat insulin type 3 times in only 3 months. That's hardly giving any one insulin a chance to be successful.
If one of my feline patients continues to need increases and gets to 6 units of cat insulin twice daily, I begin to look for causes of insulin resistance or suspect the cat injections are not being given correctly.
For example, any concurrent feline illness anywhere in the cat's body can increase the insulin requirement for a cat or make it impossible to ever find a stable dosage. The concurrent condition must be located and treated and then the insulin is more likely going to be more effective and a stable dosage can be achieved. These conditions can be such things as a feline urinary tract infection, dental disease, infection elsewhere in the body .....and many other things. The problem must be located and treated or the feline diabetes may never be controlled well enough.
The type of cat insulin given is of great importance. The source of the insulin is very important in cats. The one type that seems to work best is Beef-Pork PZI which is no longer available from Idexx, but there are compounding pharmacies that may still be able to make it.
Another thing I look for when a cat reaches 6 units of insulin and still needs more is called the Somogyi effect.
This is an odd sort of occurrence that makes it looks as if a cat is not getting enough insulin because the glucose reading is high and yet, the reverse is true. The cat has actually received too much insulin and when it drives the glucose too low, the body reacts by quickly raising the glucose to high levels.
The Somogyi effect only takes place if too much insulin is given and the way to diagnose it is with a glucose curve. This involves testing your cat's blood glucose every hour or so over the course of a day. If the Somogyi effect is occurring, it will be easy to see the glucose fall to a low level after the insulin is given and then rise quickly to levels that are too high.
In summary, the reason your cat still has high blood sugar in spite of receiving 7 units of insulin twice daily can be one of the following:
(1) The wrong type of insulin
(2) changing types of insulin too quickly without giving each increase in dosage a chance to reach it's peak effect
(3) infection or illness somewhere in the body
(4) the Somogyi effect
(5) the insulin is being stored or handled or injected incorrectly or not consistently. You should draw up the insulin and give the injection in front of your veterinarian so any problem in that area can be eliminated.
I would also like to mention that diet can be extremely helpful in lowering a cat's insulin requirements. Feeding a low carbohydrate canned food has helped many of my patients lower their insulin requirement and even lose the need for insulin altogether.
Good luck and Be Careful!
Best, Dr. Neely