Let’s talk some insulin generalities today.
U-40 insulin is more dilute than U-100 insulin. U-40 means there are 40 units per milliliter of fluid. U-100 means there are 100 units of insulin per milliliter of fluid. U-40 insulin is pretty much only a veterinary type of insulin these days. Clearly it is made at this concentration as our pets are usually smaller than humans and more dilute insulin allows more accurate dosing when using very small volumes for our smaller veterinary patients. With the advent of 3/10 cc syringes, we can use U-100 insulin on small patients, but it is clearly a smaller volume than the same amount of insulin in a U-40 concentration.
The duration of action for each insulin depends on the individual patient, but we break down insulin types into short-acting, intermediate-acting and long-acting.
In general, regular insulin is only given in emergency situations to lower the blood glucose. Regular insulin is short acting. If a pet presents in diabetic ketoacidosis, the veterinarian will likely utilize a constant rate infusion or hourly injections of regular insulin to slowly drop the blood glucose to normal levels. Once the pet is stable and eating the vet will transition the pet to a longer-acting insulin for day to day use.
The next group of insulins are the intermediate-acting insulins which are NPH and Vetsulin. Intermediate acting insulins are what we typically choose for diabetic dogs. NPH works well for many dogs, but even so it may not last the full 12 hours in between doses. That period of hyperglycemia before the next dose can result in persistent signs of urinating and drinking excessively.
Then we have longer-acting insulins: PZI, glargine (Lantus) and Detemir. Even though they are long-acting, it is a rare dog or cat that can be controlled on once daily insulin injections. Most dogs and cats will require twice daily dosing for diabetic control. Again, we typically choose intermediate-acting insulins for dogs, but if NPH and Vetsulin are unsuccessful for managing a dog’s diabetes, some vets are reaching for the longer-acting Detemir as an alternative.
When we say “basal” insulin it means it is relatively “peak-less”, or a slow sustained release. Basal long-acting insulins tend to work very well for cats. Cats tend to nibble all day compared to dogs who typically meal feed. We still give a cat a meal at the time of insulin injection, but cats may not chow it down in 2 seconds flat like the typical dog will. The commonly used long-acting basal insulins that we use for cats are glargine and PZI, but Detemir is showing promise. I am a glargine kind of vet for cats, but that is mostly because it is what I am used to. When a paper came out perhaps 8 or 9 years ago discussing insulin remission using glargine and low carb diets, I jumped on that boat! PZI is another fantastic choice for cats. I’ve had such success with Glargine and I am accustomed to how cats respond to it, so it is my go-to choice for cats. There are surely vets who feel the same way about PZI for cats. Detemir is a newer choice for cats that I’ve not personally yet used. It’s more expensive than PZI and Glargine, but may in the future be a first choice.
Hopefully this brief review will give you perspective on why veterinarians choose a particular insulin for a patient.