Shortage of ProZinc causes a scramble for feline insulin.
Update - As of September 12th, ProZinc is available again in limited supplies.
I own a busy cat practice, and we have a lot of diabetic cats in the practice. Most diabetic cats require insulin injections to achieve good control of their diabetes. Years ago, most veterinarians administered a type of insulin called protamine zinc insulin (PZI). This insulin was derived mainly from cattle. It was 90% beef, 10% pork in origin. Cats respond well to bovine insulin, because the molecular structure of feline insulin most closely resembles bovine insulin; they differ by only one amino acid. When recombinant human insulin became available, the demand for PZI insulin in humans disappeared, and it was not feasible for companies to continue to produce PZI insulin solely for use in domestic animals. Veterinarians began using recombinant human insulin to treat diabetic cats.
Currently, there are several types of insulin products available for cats with diabetes. Every practitioner has their own personal favorite. Some people use insulin glargine (brand name Lantus), while others prefer a type called protamine zinc insulin. When Lantus became available, there were high hopes that this relatively long-acting insulin could be given only once daily. Alas, this turned out to not be the case. Cats on Lantus still require twice daily insulin.