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Protamine Zinc Insulin for Dogs and Cats

By Barbara Forney, VMD

Last reviewed: 7/13/2022

Commonly prescribed for: Diabetes

Species: Dogs and Cats

Therapeutic Class: Long-acting insulin

General Drug Information and Indications

Protamine zinc insulin (PZI) is a long-acting insulin that is used in the treatment of diabetes, a relatively common disease seen in middle-aged cats and dogs. Insulin is a hormone produced by the pancreas which helps regulate blood sugar levels. Diabetic patients have high blood sugar levels (hyperglycermia). Because diabetic patients don't produce enough insulin on their own, insulin injections are given. In addition to using insulin, the successful management of your pet's diabetes requires your commitment to lifestyle and dietary management, and regular glucose testing. With appropriate management, most animals can have a normal life span.

The PZI described on this page is compounded with recombinant human insulin. PZI was recently approved by the FDA for use in cats. When the appropriate form or dose of this drug is not available through a veterinary pharmaceutical manufacturer, it may be compounded by a specialty pharmacy. PZI is also used to treat diabetes in dogs and is considered accepted practice in veterinary medicine.

How to Give this Medication

Give this medication to your pet exactly as your veterinarian prescribes. If you miss giving your pet a dose of PZI, give the next dose as soon as you remember or, if it is close to the next scheduled dose, return to the regular schedule. Do not double dose in order to catch up.

PZI is given by injection under the skin (subcutaneously). In some pets, once a day injections will be sufficient, but other animals, cats in particular, may require an injection every 12 hours. Insulin is most commonly given after a meal.

Your veterinarian will help you learn how to inject this drug under the skin. It is important to be extremely careful both with the dose measurement, and with your injection technique.

Just like in people with diabetes, the management of your pet's diet and your consistency with the insulin administration will help keep your pet's diabetes under control. Many pet owners with diabetic animals keep a supplemental supply of sugar or corn syrup with them whenever they take their diabetic animals away from home in case their pet begins to show signs of low blood sugar (hypoglycemia).

Wash your hands after giving your pet this medication.

Side Effects

Be sure to discuss any side-effects with your veterinarian immediately. The most common side effect is low blood sugar or hypoglycemia. This can be a life-threatening emergency. Because you know your pet best, you may be able to pick up the subtle changes in your pets behavior that may indicate a change in blood sugar level before it becomes a full blown emergency.

The first signs of hypoglycemia include nervousness, anxiety, weakness, trembling, loss of balance, glassy eyes or dilated pupils. If you notice these symptoms, you may be able to squirt some corn syrup on the gums or offer some food to raise blood sugar levels. Your pet should respond within one or two minutes and you should consult with your veterinarian immediately.

More severe signs of hypoglycemia include seizures, shock, and coma. If your pet is having seizures or is unconscious do not put anything (fingers or corn syrup) in your pet's mouth. Your pet will need to be admitted to a veterinary hospital immediately.


Keep this and all drugs out of reach of children. PZI is a prescription drug and should be used according to your veterinarian's directions. It should only be given to the animal for which it was prescribed. Do not give this medication to a person.

The dose of insulin is measured in units. Insulin syringe markings also measure in units. Always use the appropriate insulin syringe. U100 syringes should be used with U100 (100 units/ml) insulin. There are also some U40 (40 unit/ml) insulins and syringes. Using the wrong syringe (a U40 syringe with U100 insulin, or vice versa) will result in the wrong dose being measured and given. If you are uncertain whether the syringe you have is correct, check with your pharmacist or veterinarian before use.

Dietary changes can affect insulin requirements.

Injection site reactions may occur. If you are able to use multiple sites, the chance of a reaction will decrease.

Urinary tract infections are a common secondary problem in cats with diabetes.

Insulin may be used in pregnant animals, although breeding animals with diabetes is generally discouraged. Talk to your veterinarian about having your diabetic female cat neutered. Should your diabetic cat become pregnant, notify your veterinarian, as your pet's insulin requirements may change. Insulin may be used in animals who are nursing.

You may want to have your pet wear an identification tag that indicates that they are diabetic.

Drug Interactions

Be sure to review with your veterinarian any medications or supplements your pet may be receiving. There are multiple drug interactions with insulin.

Drugs which may increase the hypoglycemic activity of insulin (drive the blood sugar down) include: captopril, enalapril, alcohol, anabolic steroids, beta-adrenergic blockers, MAOIs, guanethidine, phenylbutazone, sulfinpyrazone, sulfonamides, tetracycline, and aspirin or other salicylates.

Drugs which may make the insulin less effective include: dextrothyroxine, dobutamine, epinephrine, estrogen/progesterone combinations, furosemide, glucocorticoids, isoniazide, phenothiazine derivatives, and thiazide diuretics.

When thyroid hormone supplementation is begun in a diabetic, hypothyroid patient, additional monitoring should be considered. Thyroid hormones may increase blood glucose levels.

Skin creams with corticosteroids can alter glucose levels in the diabetic patient and should be avoided if possible.

Diabetic patients receiving digoxin and those on diuretics should receive additional monitoring of serum potassium levels. Insulin can change serum potassium levels.


if you suspect your pet or another animal was accidentally overdosed or has eaten this medication by accident, contact your veterinarian or the A.S.P.C.A.'s Animal Poison Control Center at 888.426.4435. Always bring the prescription container with you when you take your pet for treatment.

If you or someone else has accidentally ingested this medication call the National Capital Poison Center at 800.222.1222.


Different strengths or dosage forms of PZI may have different storage requirements. Read the labeling or ask your pharmacist for the storage requirements of the prescription you receive.
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