Insulin is a standard treatment for many cats with diabetes mellitus, usually alongside a veterinarian-recommended diet, weight management where needed, and regular monitoring. Your veterinarian selects the insulin type and dose for your cat, interprets glucose and clinical results, and directs every change. Your part is to give the prescribed insulin exactly as instructed, keep accurate records, and call the clinic early when something shifts. This article explains what insulin does, how doses are set in principle, how home monitoring fits in, and which signs need urgent care. It is not a dosing guide, and none of the figures below should be used to work out a dose for your cat.
What insulin does in a diabetic cat
Diabetes mellitus means blood glucose stays persistently high because the body either produces too little insulin or does not respond to it properly, a state called insulin resistance. Insulin is the hormone that moves glucose from the bloodstream into cells, so supplying insulin brings blood glucose down. The usual warning signs are increased thirst and urination, a larger appetite alongside weight loss, lethargy, and sometimes weakness in the hind limbs.
Diagnosis does not rest on a single high number. Cats can have stress-related high blood glucose, particularly in a clinic setting, so veterinarians combine the clinical picture with blood and urine testing before reaching a diagnosis.
Insulin in the wider treatment plan
Insulin rarely works alone. Diet, weight management, and monitoring all influence how much insulin a cat needs, and your veterinarian adjusts them together.
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Some newly diagnosed cats enter diabetic remission and no longer need insulin. Remission is judged by the veterinary team from glucose monitoring and clinical signs, not from how well the cat appears at home. Until your veterinarian confirms otherwise, keep giving insulin on the prescribed schedule, and do not stop it or change its timing, dose, or the cat’s diet on your own.
Which insulins are used
The Merck Veterinary Manual describes PZI and glargine as the insulins commonly used for newly diagnosed cats, and says they produce comparable glycemic control and remission rates. It does not recommend NPH or porcine zinc lente as initial treatment, citing their short duration and poor control of clinical signs in many cats. Product availability and labeling differ by country and change over time, so the product name on your cat’s prescription label is the one to follow.
| Insulin | Status in Merck Veterinary Manual guidance | Key point |
|---|---|---|
| PZI (protamine zinc insulin) | Commonly used in newly diagnosed cats | Long-acting; described as giving comparable glycemic control and remission rates to glargine |
| Glargine | Commonly used in newly diagnosed cats | Long-acting; described as giving comparable glycemic control and remission rates to PZI |
| NPH (neutral protamine Hagedorn) | Not recommended as initial treatment | Short duration and poor control of clinical signs in many cats |
| Porcine zinc lente | Not recommended as initial treatment | Same concerns as NPH: short duration and poor control of clinical signs in many cats |
What your veterinarian weighs
Choosing an insulin is a clinical judgment. Your veterinarian is likely to consider:
- How long the insulin acts and how the cat has responded to any earlier treatment
- How many injections per day your household can give consistently
- Other conditions the cat has and the medicines it already takes
- How much home monitoring you can realistically carry out
- Whether glucose meters, strips, or sensors fit the chosen plan
- Whether you can attend rechecks on the schedule the plan needs
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- ACCURATE DOSING: Bold, smudge-resistent unit markings and large, easy-grip barrel flanges help provide precise dosing when every unit matters.
- 100 PET INSULIN SYRINGES: Each box contains 100 single-use 1/2cc U-40 insulin syringes with polished, silicone-coated 1/2-inch needles. Compatible with Vetsulin and Prozinc. Doses up to 20 units of U-40 insulin.
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How the dose is set
There is no standard dose for every cat. The starting dose is calculated from the cat’s weight, then adjusted using monitoring results and clinical signs. Professional guidance publishes reference examples to show how that reasoning works. They are not instructions for calculating or giving a dose at home, and they do not replace your veterinarian’s written plan.
The Merck Veterinary Manual page does not display a publication year, so check its current wording before relying on its figures. The American Association of Feline Practitioners (AAFP) diabetes toolkit uses a different framing for initiating treatment, which is one reason the written plan matters more than any single published number.
| Reference source | Insulin | Example starting approach | Early review |
|---|---|---|---|
| Merck Veterinary Manual | PZI | 0.25 U/kg (about 1 U per cat), given subcutaneously every 12 hours, using estimated ideal body weight | Re-evaluate after 5–7 days |
| Merck Veterinary Manual | Glargine | 0.25–0.5 U/kg (about 1–2 U per cat) every 12 hours | Re-evaluate after 5–7 days |
| AAFP diabetes toolkit | Not stated for this protocol | 0.25–0.5 U/kg every 12 hours; often 1 U per cat every 12 hours for average cats | Recheck 5–10 days after starting (standard approach) |
Why starting doses are kept conservative
- Merck advises using estimated ideal body weight rather than actual weight, which ties the starting point to the cat’s lean size rather than to excess weight.
- Its example approach keeps starting doses conservative and does not go above 2 U per cat.
- It recommends re-evaluating after 5–7 days, and avoiding dose increases more often than every 1–2 weeks unless low blood glucose prompts earlier action.
- AAFP protocols adjust doses in 0.5-unit steps.
Questions to have answered in writing
Before your first home injection, ask your veterinarian to give you these details in writing:
- The exact insulin product, its concentration, and the syringe type that matches it
- The dose in units, the injection times, and what to do if a dose is missed
- Which glucose readings to take, when to take them, and the target range for your cat
- When the next recheck is due and which results would prompt an earlier call
- What to do if your cat is not eating normally on injection day
- The after-hours number to call and the nearest emergency clinic
Monitoring at home
Monitoring shows whether the current dose fits your cat. Veterinarians may use a glucose curve (readings taken across a day in the clinic), spot readings, home blood glucose measurements, a continuous glucose monitor (CGM), fructosamine, and clinical signs. Interpreting those results and deciding whether the dose changes is the veterinarian’s job. Home readings can better reflect your cat’s normal life, because clinic stress can itself raise glucose.
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- HALF-UNIT MARKINGS: Dose unit markings in half-unit increments for pets who require small or half-unit doses. FOR ANIMAL USE ONLY.
- SILICONE LUBRICATION: A layer of microbonded silicone lubrication helps the fine 29-gauge needle glide smoothly into the skin, for a more comfortable insulin injection for your diabetic dog or cat.
- MICRO-POLISHED FOR SMOOTHER INJECTION: Each triple-bevel needle is micro-polished to remove blemishes, reducing friction during injection. Made with durable materials for everyday safety.
- ACCURATE DOSING: Bold, smudge-resistent unit markings and large, easy-grip barrel flanges help provide precise dosing when every unit matters.
- 100 PET INSULIN SYRINGES: Each box contains 100 single-use 3/10cc U-40 insulin syringes with polished, silicone-coated 1/2-inch needles. Compatible with Vetsulin and Prozinc. Doses up to 12 units of U-40 insulin.
The AAFP toolkit describes three monitoring approaches. Its numbers are protocol examples rather than universal schedules, and your veterinarian sets the targets for your individual cat.
| AAFP toolkit approach | What it involves | Who it suits |
|---|---|---|
| Intensive | Home glucose checks before each injection and 6–10 hours after the morning dose; intensive-monitoring target of 80–220 mg/dL (4.4–12.3 mmol/L) | Caregivers able to test reliably at those times; decided with your veterinarian |
| Standard | Recheck 5–10 days after starting; glucose curve with follow-up every 5–7 days until stable, then every 3–6 months | Depends on the cat’s condition and what your household can manage; decided with your veterinarian |
| Clinical-sign-based | Adjustments guided mainly by appetite, energy, thirst, and urination; specific schedule and targets not stated in the toolkit | Depends on the cat’s condition and caregiver capacity; decided with your veterinarian |
What each test tells the team
- Fructosamine reflects average glucose over roughly the preceding 7–14 days, so it does not reveal a recent change.
- Urine glucose is not a sensitive tool for guiding dose changes.
- Urine ketones can help assess risk.
Meters, strips, and sensors
Ask the team which glucose meter, test strips, or CGM sensor they want you to use. Strip and sensor compatibility depends on the device, so do not mix components from different systems, and have the team show you how to use the chosen device before you rely on it.
What to record each day
A consistent log is often the most useful thing you can bring to a recheck. Record:
- Each dose and the time it was given
- Meals and how much the cat actually ate
- Water intake and urine output
- Energy, grooming, appetite, and any new behavior
- Weight, measured on the same scale at similar times
- Any glucose readings, with the time relative to the last injection
If readings or behavior move outside what the team has described, call them rather than adjusting insulin yourself.
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- SILICONE LUBRICATION: A layer of microbonded silicone lubrication helps the fine 29-gauge needle glide smoothly into the skin, for a more comfortable insulin injection for your diabetic dog or cat.
- MICRO-POLISHED FOR SMOOTHER INJECTION: Each triple-bevel needle is micro-polished to remove blemishes, reducing friction during injection. Made with durable materials for everyday safety.
- ACCURATE DOSING: Bold, smudge-resistent unit markings and large, easy-grip barrel flanges help provide precise dosing when every unit matters.
- 100 PET INSULIN SYRINGES: Each box contains 100 single-use 3/10cc U-100 insulin syringes with polished, silicone-coated 1/2-inch needles. Doses up to 30 units of U-100 insulin.
- PREMIUM QUALITY ULTICARE VETRX SYRINGES: Triple-bevel, electromagnetic-polished, silicone-coated needles with bold barrel markings for accurate, confident dosing. Subscribe & Save available. FOR ANIMAL USE ONLY.
Giving insulin safely
Match the syringe to the insulin concentration
Insulin is sold in different concentrations, and syringes are calibrated for one of them. Merck states that U-40 syringes are typical for long-acting veterinary insulins such as PZI and glargine used in cats, and VCA discusses both U-40 and U-100 products. A syringe of the wrong concentration delivers the wrong number of units, which is a serious dosing error. Do not substitute a syringe of a different concentration, even if it is the one you already have at home.
Before your first home injection:
- Read the concentration printed on the insulin label, for example U-40.
- Confirm that the syringe packaging states the same concentration.
- Ask the veterinary team to watch you draw up and inject a dose with that exact syringe.
- Ask whether your product needs mixing, and have the team show you the method for that specific product.
Storage and handling
VCA advises refrigerating insulin and avoiding freezing, direct sunlight, and high temperatures. Some preparations must be mixed before use and the method differs by product, so follow the label and the team’s demonstration rather than a general rule.
When your cat is not eating
Reduced appetite or a change in food intake can change how much insulin a cat needs. Call the veterinary team for instructions rather than guessing whether to give the usual dose.
Low blood sugar: signs that need immediate action
Too much insulin relative to the cat’s food intake and body needs can cause hypoglycemia, which can be life-threatening. Merck lists these warning signs:
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- Weakness
- Lack of coordination, such as stumbling or unsteady walking
- Seizures
- Collapse
Treat any of these as an emergency. Contact your veterinarian immediately, or the nearest emergency clinic if the practice is closed. Do not wait to see whether your cat recovers on its own.
Make the low-sugar plan before you need it
Ask your veterinarian to write down what you should do at home if you suspect low blood sugar, which number to call, and where the nearest emergency clinic is. Keep that plan with the insulin and your log.
Ketoacidosis: when untreated diabetes becomes an emergency
Untreated or poorly controlled diabetes can progress to diabetic ketoacidosis (DKA), which requires immediate veterinary treatment. Lethargy, weakness, poor appetite, and trouble breathing, especially alongside increased thirst or urination, call for prompt veterinary evaluation rather than a wait-and-see approach.
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