The label says, word for word:
PROZINC (protamine zinc recombinant human insulin) is indicated for the reduction of hyperglycemia and hyperglycemia-associated clinical signs in cats with diabetes mellitus. PROZINC (protamine zinc recombinant human insulin) is indicated for the reduction of hyperglycemia and hyperglycemia-associated clinical signs in dogs with diabetes mellitus.
PROZINC is contraindicated in cats sensitive to protamine zinc recombinant human insulin or any other ingredients in PROZINC. PROZINC is contraindicated during episodes of hypoglycemia.
For use in cats and dogs only. Keep out of the reach of children. Avoid contact with eyes. In case of contact, immediately flush eyes with running water for at least 15 minutes. Accidental injection may cause hypoglycemia. In case of accidental injection, seek medical attention immediately. Exposure to product may induce a local or systemic allergic reaction in sensitized individuals.
Owners should be advised to observe for signs of hypoglycemia (see Client Information Sheet). Use of this product, even at established doses, has been associated with hypoglycemia.
Any change in insulin should be made cautiously and only under a veterinarian's supervision.
Overdose can result in profound hypoglycemia and death.
The safety and effectiveness of PROZINC in kittens has not been evaluated.
From the sheet the maker writes for owners:
Approved by FDA under NADA # 141-297; original approval October 28, 2009 for cats (FOI summary; sponsor Boehringer Ingelheim Vetmedica, Inc.); a supplemental approval dated February 8, 2019 added dogs (FDA: "The most common adverse reactions in dogs taking ProZinc were lethargy, anorexia, hypoglycemia, vomiting, seizures, shaking, diarrhea, and ataxia."). Label revised 08/2019.
The emergency page sorts the signs by how long you have, and the symptom checker asks what you are seeing. Reactions to a medicine can also be reported to the FDA yourself: how to report a problem.
These answers come from the approved label on DailyMed, read on 2 October 2026. Where the label does not say, the answer says so, and the vet or the pharmacist is the one to ask.
The approved use is quoted at the top of this page. It is an insulin for cats and dogs with diabetes: the label says it reduces high blood sugar and the signs that come with it.
The label gives no time for cats. For dogs, it reports a study in 10 healthy Beagles in which the insulin began to act between half an hour and 14 hours after the injection, and blood sugar reached its lowest point between 5 hours and more than 24 hours after it. The label notes that the curves varied from dog to dog, and the owner sheet says follow-up visits and testing show whether the dose needs changing.
It is an injection under the skin that the owner gives at home, once the vet has shown how. The label says to give it with or right after a meal, to mix it by gently rolling the vial, never shaking it, until it looks evenly white and cloudy, and to use only U-40 syringes, because any other syringe gives the wrong amount. The owner sheet says not to use it, and to call the vet, if clumps or white particles are still there after rolling. It also says not to give the dose if your pet is not eating, is vomiting, or is having an episode of low blood sugar.
The owner sheet that comes with the label answers this. If an injection is missed, or your pet gets less than the prescribed dose, contact the vet as soon as possible for advice on the next dose. If you cannot reach the vet and your pet is eating and acting normally, give the usual dose at the next regularly scheduled injection time. If you inject more than the prescribed amount, the sheet says to contact the vet immediately, and another vet if yours is not available.
The studies and the warnings are quoted above. The owner sheet says to contact the vet immediately if you think your pet has a medical problem or a side effect. The most common one is low blood sugar, which it says can come on suddenly, with weakness, sluggishness, a staggering walk, changes in behavior, muscle twitching, seizures or coma. A pet that is unconscious or having a seizure is a medical emergency, and the sheet says to take it to the vet immediately. For a pet that is conscious, it says to rub about a tablespoon of corn syrup or honey on the gums, feed the usual meal once your pet is alert enough to eat, and contact the vet.
Store the vial upright in a refrigerator at 36° to 46°F; do not freeze it, and protect it from light. The smaller vial is to be used within 60 days of the first puncture and the larger vial within 80 days. Keep it out of the reach of children. If a person is injected by accident, the label says to seek medical attention immediately.
The FDA says the best way to get rid of most unused or expired medicines is a take-back option: a drug take-back location, which can be at a pharmacy or a police station, or a prepaid mail-back envelope. If you cannot use one and the medicine is not on the FDA's flush list, the FDA says to mix it with something unappealing such as dirt, cat litter or used coffee grounds and to seal the mixture in a plastic bag before throwing it away. Flushing is only for medicines on that list, such as opioids. The label does not say how to get rid of used syringes and needles, so ask the clinic or the pharmacy. Do not give leftovers to another pet.
Write the dose, the times and the stop date here, then print this page for the fridge.
Dose and times: _____________________________________________
Stop date: _____________________________________________
The 2026 dog diabetes guideline, in plain English: what well controlled actually means, every insulin with its starting dose, the syringe that has to match the bottle, the meal rule, and what to do when the sugar goes too low. Diabetes in dogs.