Protamine zinc insulin (PZI) is a long-acting, injectable insulin preparation formulated to release slowly over a prolonged period. While this insulin was developed for human use, its application today is almost exclusively in veterinary medicine for managing diabetes mellitus in companion animals.
How Protamine Zinc Insulin Works
The extended duration of PZI is achieved by adding two substances: protamine and zinc. Protamine is a simple protein, and when combined with insulin and a small amount of zinc, it changes the insulin’s solubility. This alteration causes the insulin to form microscopic crystals at the subcutaneous injection site.
The crystalline structure dissolves gradually over many hours. This slow dissolution results in a steady, prolonged release of insulin into the body. The result is a duration of action that can last from 6 to 28 hours in dogs and 7 to 18 hours in cats.
Veterinary Use in Diabetes Management
PZI is frequently used in the management of diabetes in cats and is also prescribed for dogs. The slow, steady release of insulin from PZI is particularly well-suited to the metabolism of many diabetic cats, helping to control high blood sugar (hyperglycemia). Feline diabetes often resembles Type 2 diabetes in humans, and PZI can be effective for maintaining glycemic control throughout the day, often with just one or two daily injections.
For both cats and dogs, the primary goal of PZI therapy is to stabilize blood glucose levels and reduce the associated clinical signs, such as excessive thirst and urination. By providing a consistent background level of insulin, PZI helps to prevent the dramatic peaks and troughs in blood sugar that can occur with shorter-acting insulins. A common brand name for veterinary PZI is ProZinc®, which is a human recombinant insulin approved for use in both species.
Administration and Potential Side Effects
PZI is administered as an injection just under the skin, known as a subcutaneous injection. It is important for pet owners to use the correct type of syringe, a U-40 syringe, to ensure accurate dosing. Before drawing the dose, the vial should be gently rolled between the hands to mix the contents; it should never be shaken, as this can damage the insulin molecules and alter their effectiveness.
The most significant risk with insulin therapy is hypoglycemia, or low blood sugar. If any of these signs are observed, it is an emergency, and a veterinarian should be contacted immediately. Signs of hypoglycemia in pets include:
- Weakness
- Lethargy
- Stumbling
- Behavioral changes
- Muscle twitching
- Seizures
Adhering strictly to the veterinarian’s prescribed dose and feeding schedule is fundamental to minimizing the risk of this serious side effect.