Most cats with diabetes start on 0.25 to 0.5 units of insulin per kilogram of lean body weight, given twice daily. For an average-sized cat weighing around 5 kg (11 pounds), that typically works out to roughly 1 to 2.5 units per injection. Your veterinarian will set the exact starting dose based on your cat’s weight, overall health, and blood sugar levels, then adjust it over several weeks based on how your cat responds.
Starting Doses for Common Insulin Types
Three insulin products are most widely used in cats: ProZinc (protamine zinc insulin), Lantus (glargine), and Levemir (detemir). All three share the same recommended starting range of 0.25 to 0.5 units per kilogram, given every 12 hours. The dose is calculated using lean body weight, meaning excess fat isn’t factored in. An overweight cat that should weigh 5 kg gets dosed for 5 kg, not their actual scale weight of 7 kg.
Lantus tends to have the longest duration of action in cats. In studies of healthy cats, a single dose suppressed blood sugar for at least 24 hours in about half the animals tested, with peak effect around 14 hours after injection. Lente insulin (sold as Vetsulin or Caninsulin) wears off faster, leaving roughly 8 hours each day where it provides minimal blood sugar control. This is one reason many veterinarians now prefer glargine or ProZinc for cats.
Why the Right Syringe Matters
This is one of the most common sources of dangerous dosing errors. ProZinc and Vetsulin are formulated at 40 units per milliliter (U-40), while Lantus and Levemir are formulated at 100 units per milliliter (U-100). If you draw up a U-40 insulin using a U-100 syringe, you’ll give less than half the intended dose. If you accidentally use a U-40 syringe with a U-100 insulin, you could give 2.5 times too much.
Always match the syringe to the insulin concentration. U-40 insulin gets a U-40 syringe. U-100 insulin gets a U-100 syringe. If your vet switches your cat’s insulin type, confirm whether you also need new syringes.
How Doses Get Adjusted
The starting dose is just a starting point. Your vet will fine-tune the dose using blood glucose curves, which involve measuring your cat’s blood sugar every 2 to 3 hours over a 12-hour period (or 24 hours if insulin is given once daily). Some owners learn to do these curves at home with a pet glucometer, which gives a more accurate picture since many cats run high blood sugar from stress at the clinic.
The target range during a glucose curve is a lowest reading (called the nadir) between 80 and 150 mg/dL. The highest reading during the day should ideally stay close to 300 mg/dL or below. If blood sugar drops below 80 mg/dL at any point, the insulin dose needs to be reduced, regardless of what the other readings look like. Dose changes are typically small, around 0.5 to 1 unit at a time, and are made no more frequently than every one to two weeks to allow the cat’s body to stabilize.
How Diet Affects Insulin Needs
What your cat eats has a direct impact on how much insulin it needs. A study comparing cats on a low-carbohydrate diet (12% of calories from carbs) to cats on a moderate-carbohydrate diet (26% of calories from carbs) found striking differences. After 16 weeks, 68% of cats eating the low-carb food no longer needed insulin at all, compared to 41% of cats on the moderate-carb diet.
This is why most vets now recommend a high-protein, low-carbohydrate canned food for diabetic cats. Dry kibble tends to be much higher in carbohydrates. Switching to a low-carb wet food can reduce insulin requirements significantly, and in some cases, push cats into full remission where they no longer need injections. If you make a diet change, your vet will need to monitor blood sugar closely, because the insulin dose may need to come down quickly to avoid dangerous lows.
Recognizing Low Blood Sugar
Hypoglycemia is the most immediate risk of insulin therapy, and giving too much insulin is the most common cause. Signs include weakness, lethargy, vomiting, loss of coordination, tremors, seizures, and in severe cases, coma. If you notice any of these, offer your cat food right away. If your cat won’t eat voluntarily, rub honey, corn syrup, or a dextrose gel (available at most pharmacies) onto the gums and contact your vet immediately.
Do not put your fingers or force anything into the mouth of a cat that is seizing or unconscious. Rubbing a sugar source on the outer gums is enough to raise blood sugar while you get to the vet. Hypoglycemia can be fatal if untreated, so this is the one emergency every diabetic cat owner should be prepared for. Keeping a bottle of corn syrup near the insulin supplies is a simple precaution.
Storing Insulin Properly
All insulin vials should be kept refrigerated. Manufacturers recommend using opened vials within 28 to 56 days for most human insulin products, or up to 80 days for the larger ProZinc vials. In practice, a study that tracked refrigerated vials of both Lantus and ProZinc over six months of routine household use found no bacterial contamination and no loss of sterility. Still, potency can gradually decline, so if your cat’s blood sugar control seems to worsen after a vial has been open for a couple of months, a fresh vial may help.
Gently roll the vial between your hands before drawing up a dose, especially with ProZinc and Vetsulin, which are suspensions that settle. Never shake insulin vials, as this can damage the protein and reduce effectiveness.
What Remission Looks Like
Unlike dogs, cats with diabetes have a real chance of going into remission, meaning their blood sugar returns to normal without insulin. This happens most often when treatment starts early, when a low-carb diet is introduced, and when blood sugar is kept well-controlled from the beginning. Remission rates vary, but studies show anywhere from 40% to 68% of cats can achieve it depending on diet and how quickly treatment is optimized.
If your cat goes into remission, you’ll still need to monitor for relapse. Some cats stay off insulin permanently, while others need it again months or years later. Regular blood sugar checks, even after insulin is stopped, help catch any return of diabetes before it causes problems.