My response:
The rising cost of all of the human insulin analogs, such as glargine and detemir, are indeed becoming a problem for many owners. If you and the owner decide to switch to another insulin preparation, you have 4 insulin preparations that could be considered (all should be given twice a day):
1. Levemir (insulin detemir), another long-acting human insulin analog
2. ProZinc (Protamine Zinc Insulin; PZI), a long-acting veterinary insulin preparation
3. Humulin N or Novolin N (NPH insulin), an intermediate-acting human insulin preparation
4. Vetsulin (porcine insulin zinc suspension; lente), an intermediate-acting veterinary insulin preparation
Cost comparison
Levemir (detemir): As far as cost, the retail price of Levemir will be about the same or even more than glargine (~$200 per vial), so that's not a good option for this owner.
ProZinc (PZI): A 10-mL vial of ProZinc insulin will be a bit cheaper than either a 10-mL vial of glargine or detemir. Most veterinarians will charge ~$125 - $150 for a vial of ProZinc, whereas both glargine and detemir will be ~$200 or more. That said, ProZinc is certainly not an inexpensive insulin preparation, especially when one considers that ProZinc is a U-40 insulin and each vial contains only 400 units of insulin. Since both glargine and detemir are U-100 insulins, a vial of these insulin preparations will contain 1,000 units of insulin. Therefore, the cost of ProZinc, at least per unit of insulin, turns out to be even more than the human insulin analogs.
Humulin/Novolin-N (NPH): The retail prices of an individual vial of NPH insulin (U-100) will vary widely depending on the pharmacy and its location. At the moment, the least expensive NPH product is Walmart's ReliOn brand (a Novolin insulin), which is sold at ~$25 per vial. However, most other pharmacies charge a retail price of $60 to $100 per vial. So if you consider the cost per ml of insulin, NPH insulin would be the cheapest. However, NPH insulin is also the least effective insulin in cats because of its very short duration, so I would not recommend this insulin in any cat, especially if excellent glycemic control or remission is the goal.
Vetsulin (porcine insulin zinc suspension): Vetsulin is available as a 10-mL vial of insulin in a U-40 insulin concentration. For veterinarians, the wholesale cost of the Vetsulin product is inexpensive (~$25 per vial). In most veterinary practices, the retail price of a vial of Vetsulin sold to pet owners will be approximately $50.
Therefore, the cost of a bottle of Vetsulin is similar or even less than the price of NPH insulin and costs much less (about 25-30%) than that of insulin glargine or detemir. But again, the total amount of insulin in a vial of NPH, glargine, and detemir (all U-100 insulins) is 1000 units, where a vial of Vetsulin (a U-40 insulin) contains 400 units, only 40% as much. So in the end, the client cost per unit of Vetsulin would be similar or slightly more than NPH but much less than Lantus, Levemir, or ProZinc.
Effectiveness of insulin preparations in cats
One must remember that it doesn't matter how much money we are saving if the insulin isn't working to control hyperglycemia and prevent ketoacidosis.
Most veterinarians would rank insulin glargine as the first choice of insulin in cats, then insulin detemir or PZI (not the compounded product (1), but FDA-approved ProZinc), then Vetsulin, then finally human NPH insulin as a very last choice (2-10). In my experience, all of the long-acting insulin preparations will show a similar effectiveness and remission rates (~35-50%), although individual cats may respond much better to one of these insulin products.
A number of studies have proven that Vetsulin will certainly control hyperglycemia in cats, especially if combined with a low carbohydrate diet (9,10). The remission rates for Vetsulin, on average, will not be as high as the long-acting insulins, but remission can certainly occur in cats on this insulin.
In this cat, however, remission of the diabetic state is highly unlikely. Most cats will go into remission within 3 months of starting insulin therapy (11-14). If the diabetic state has persisted for longer than 6 months, remission is highly unlikely. This is especially true in diabetic cats like your patient, in which an underlying cause of insulin resistance (i.e., obesity) is present.
Bottom Line
In this cat, given that remission has not occurred after 1-year of therapy with glargine and a low-carbohydrate diet, I would go with the least expensive insulin that will likely be effective in maintaining glycemic control and preventing ketoacidosis. Overall, the best insulin fitting those criteria would be Vetsulin, which is relatively inexpensive and certainly would be more than adequate in most diabetic cats.
