# Vetsulin for Cats: Dosing, Syringes, and Alternatives Vetsulin is a U-40 insulin made for dogs and cats, and it is given by injection under the skin, usually twice a day. Your veterinarian sets the dose based on your cat's weight, blood glucose, and response to treatment, and you measure that dose with a U-40 syringe matched to the insulin. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Quick Answer - Vetsulin is a U-40 insulin, so it must be measured with U-40 syringes. Using a U-100 syringe with Vetsulin gives the wrong dose. - Never change your cat's dose on your own. The veterinarian calculates it from weight, blood glucose readings, and how your cat responds. - Give the injection under the skin, usually twice daily at about the same times each day, and rotate injection sites. - Store Vetsulin according to the label directions, keep it out of extreme heat and freezing, and check the expiration date. - If you miss a dose, do not double up. Call your veterinarian for instructions. ## What Vetsulin Is and What Veterinarians Use It For Vetsulin is an injectable insulin product labeled for use in dogs and cats with diabetes mellitus. It is a porcine (pig) origin insulin with an intermediate duration of action, which means it is designed to cover a cat's insulin needs for roughly half a day. That is why most cats on Vetsulin receive two injections per day. Feline diabetes happens when a cat cannot produce enough insulin or cannot use insulin properly, so glucose builds up in the blood. Insulin injections replace or supplement what the body is missing. Insulin remains the standard of care for feline diabetes, even as non-insulin options have entered the picture [1]. Vetsulin is one of several insulin choices for cats. It is not automatically the best choice for every cat. The right insulin depends on the individual cat's clinical situation, including how much insulin-producing capacity the cat still has [2]. ## How Vetsulin Works Insulin moves glucose from the bloodstream into cells, where it is used for energy. When a diabetic cat gets an injection, blood glucose starts to fall, reaches a low point, then rises again as the insulin is used up. The goal is to keep glucose in a safer range for as much of the day as possible without dropping too low. Insulin types differ in how steady their effect is. Some insulins act as a basal insulin, meaning their effect is roughly the same hour after hour. In cats that still have some working beta cells, a basal insulin alone may bring blood glucose all the way back to normal [2]. Only insulin glargine U300 comes close to that steady, flat profile in cats [2]. Vetsulin has a more peaked action, which suits some cats and not others. Your veterinarian will use blood glucose curves, home monitoring, or a continuous glucose monitor to see how your cat responds and to adjust the plan. ## Vetsulin Instructions for Cats: Dosing Basics ### Who decides the dose Your veterinarian decides the starting dose and every change after that. Doses are calculated from your cat's body weight, current blood glucose, clinical signs, and how the cat responded to the previous dose. There is no single dose that fits all cats, and the correct dose for your cat can change over time. Never adjust the dose because a reading looks high or low on a home meter. A single number can be misleading, and insulin changes are based on patterns, not one value. ### How the injection is given Vetsulin is given as a subcutaneous injection, which means under the skin. Common sites are the scruff between the shoulder blades, the side of the chest, or the flank. Rotate sites so the same spot is not used every time. Use a fresh needle for each injection. Draw the dose carefully, check for air bubbles, and confirm the syringe markings before you inject. If your cat squirms or you are unsure the full dose went in, do not give a second injection. Note what happened and tell your veterinarian. If your cat is hard to medicate in general, some of the same handling techniques used for oral medicines can help you stay calm and steady. See [How to Give Your Cat Liquid Medicine Without a Syringe: Alternative Methods](/knowledge/veterinary-medicine/pet-medication-guide/give-cat-liquid-medicine-without-syringe) for practical positioning tips. ### Vetsulin syringes for cats Vetsulin is a U-40 insulin. Vetsulin syringes for cats are also U-40, so the markings on the barrel match the concentration in the vial. This matters more than almost anything else in diabetes care. If you draw Vetsulin into a U-100 syringe, the markings will not match the insulin, and your cat will get the wrong amount. U-100 syringes are made for U-100 insulins, which are more concentrated. Check your syringes before every dose. Look for the U-40 marking on the package and the barrel. If your pharmacy gives you a different type, call your veterinarian before using it. Also check needle length and gauge with your vet, since very short needles may not deliver the dose reliably under the skin. Never mix Vetsulin with another insulin in the same syringe unless your veterinarian specifically tells you to. ### Missed doses If you miss a dose, do not give a double dose at the next scheduled time. Call your veterinarian or your emergency clinic for guidance. They may tell you to skip the missed dose and resume the normal schedule, or they may adjust the plan based on how long it has been and how your cat is acting. If you are unsure whether the injection went in, treat it as a possible missed dose and ask before repeating it. ### Storage Follow the storage directions on the Vetsulin label and the instructions from your veterinarian. In general, insulin should be kept out of freezing temperatures and out of direct heat. Do not use insulin that has been frozen, has changed color, or contains clumps or particles. Check the expiration date before each new vial, and write the date you opened it on the box. ## Side Effects of Vetsulin in Cats | Side effect | How common or serious | What to do | |---|---|---| | Low blood glucose (hypoglycemia): weakness, wobbling, drooling, confusion, collapse, seizures | Serious and potentially life threatening | Treat as an emergency. Call your veterinarian or an emergency clinic right away | | High blood glucose that does not improve: increased thirst, urination, appetite, weight loss | Common when the dose is too low or the insulin is not lasting | Report the signs to your veterinarian for a dose or insulin review | | Injection site reactions: pain, swelling, thickening of the skin | Uncommon but possible | Tell your veterinarian and rotate injection sites | | Poor appetite, vomiting, lethargy | Can signal a serious problem such as ketoacidosis | Contact your veterinarian the same day | | Allergic reactions: facial swelling, hives, difficulty breathing | Rare but serious | Seek emergency veterinary care immediately | Hypoglycemia is the side effect that worries veterinarians most, because it can become severe quickly. If your cat is alert and able to swallow, your veterinarian may have you apply a sugar source such as corn syrup or honey to the gums. If your cat is unconscious, having seizures, or cannot swallow, go to an emergency clinic now. ## Who Should Not Take Vetsulin and Drug Interactions Vetsulin is not right for every diabetic cat. Your veterinarian will consider your cat's other health conditions, current medications, and how well you can monitor and inject at home before choosing an insulin. Cats with certain concurrent illnesses, cats that have had severe hypoglycemic episodes, and cats whose owners cannot safely give injections may be better served by a different plan. Tell your veterinarian about every medication, supplement, and topical product your cat receives, including flea and tick products. Some drugs can raise or lower blood glucose and change insulin requirements. If your cat takes other medications, ask your veterinarian whether any of them affect blood sugar. For general guidance on which human products are safe around cats, see [What Human Medications Are Safe for Cats? A Vet's Guide to OTC Options](/knowledge/veterinary-medicine/vet-visit-decisions/human-medications-safe-for-cats). Never give a human diabetes drug to your cat. ## Overdose and When to Call a Veterinarian or Poison Control An insulin overdose can cause dangerously low blood glucose. Signs include wobbling, weakness, drooling, twitching, collapse, and seizures. This is a medical emergency. If you think your cat received too much Vetsulin, call your veterinarian or an emergency veterinary clinic immediately. If your regular clinic is closed, go to the nearest emergency hospital. You can also call poison control for guidance: - ASPCA Animal Poison Control Center: (888) 426-4435 - Pet Poison Helpline: (855) 764-7661 Do not wait for symptoms to appear before you call. Bring the insulin vial, the syringe, and the packaging with you if you go to a clinic, so the team knows exactly what was given. ## Vetsulin Alternatives for Cats Vetsulin is one option among several. Your veterinarian may switch your cat to a different insulin if blood glucose stays high, if lows keep happening, if the twice-daily schedule is not working for your household, or if your cat's other health conditions change. Insulin glargine U300 is the insulin that comes closest to a steady, flat, basal profile in cats, which can be a good fit for cats that still produce some of their own insulin [2]. Other insulin formulations are also used in feline diabetes, and the choice should be matched to the specific cat instead of picked by default [2]. Non-insulin antidiabetic drugs are also available. SGLT2 inhibitors such as bexagliflozin and velagliflozin have shown high treatment success rates and results non-inferior to insulin in cats, but they carry a significant risk of euglycemic diabetic ketoacidosis, a serious complication [1]. Bexagliflozin is given as an oral tablet, and one pharmacokinetic study in healthy cats found rapid absorption after oral dosing with a terminal half-life of about 6.9 hours and absolute bioavailability of 78% [3]. Older drugs such as glipizide, metformin, and acarbose have shown limited efficacy in diabetic cats, based on evidence with a high risk of bias [1]. These drugs are not interchangeable with insulin, and they are not right for every cat. Some cats cannot use them at all. Your veterinarian will decide whether an alternative fits your cat. Veterinarians weigh the cat's wellbeing, your ability to manage care at home, and the practical realities of daily treatment when choosing a plan [4]. If the current plan is not working for you or your cat, say so. There is often another option. ## Limitations and When to Contact a Veterinarian This article covers general principles. Your cat's dose, monitoring schedule, and insulin choice depend on details only your veterinarian knows. Individual cases need a veterinarian. Contact your veterinarian the same day if your cat: - Has blood glucose readings that are consistently higher than the target range - Is drinking and urinating much more than usual - Is eating less or losing weight - Has vomiting, diarrhea, or unusual lethargy - Has a suspected missed dose or a dose you are unsure about Go to an emergency clinic now if your cat: - Is weak, wobbly, drooling, twitching, or collapsing - Has a seizure - Is unconscious or cannot be woken - Is breathing hard or has facial swelling - Has severe vomiting with no interest in food, which can signal ketoacidosis Keep routine recheck visits even when your cat seems fine. Diabetes control changes over time, and regular monitoring is how problems get caught early. ## Frequently Asked Questions ### Can I use a U-100 syringe with Vetsulin? No. Vetsulin is a U-40 insulin, so it must be measured with U-40 syringes. A U-100 syringe has different markings and will not deliver the intended dose. If you are unsure which syringes you have, call your veterinarian or pharmacist before the next injection. ### What should I do if I miss a Vetsulin dose? Do not give a double dose to make up for it. Call your veterinarian for instructions, since the right step depends on how long it has been and how your cat is doing. If you are not sure whether the injection went in, treat it as a possible miss and ask. ### Can my cat's Vetsulin dose be changed at home? No. Dose changes are based on blood glucose patterns, clinical signs, and your cat's overall health, and your veterinarian makes those calls. Changing the dose on your own can cause dangerous low blood glucose or leave diabetes poorly controlled. Report any concerns and let your vet adjust the plan. ### Why would my veterinarian switch my cat off Vetsulin? Vetsulin may not control every cat well, and some cats do better on a different insulin or a non-insulin drug. Insulin glargine U300 has a steadier action in cats, and SGLT2 inhibitors have shown strong results in some cats but carry a risk of euglycemic diabetic ketoacidosis [2][1]. The decision depends on your cat's response and your home situation. ### Is Vetsulin the best insulin for cats? No single insulin is best for every cat by default. The choice should be tailored to the individual cat's clinical situation, including how much insulin the cat still produces on its own [2]. Talk with your veterinarian about what fits your cat and your daily routine. ### Can I give my cat human diabetes medication instead of Vetsulin? No. Human diabetes drugs are not a substitute for veterinary insulin, and some can cause serious harm in cats. If cost or convenience is a concern, ask your veterinarian about options instead of improvising. For general safety guidance on human products around cats, see [What Human Medications Are Safe for Cats? A Vet's Guide to OTC Options](/knowledge/veterinary-medicine/vet-visit-decisions/human-medications-safe-for-cats). ## Related Articles - [Can I Give My Cat Melatonin? Safety, Dosage, and When to Avoid It](/knowledge/veterinary-medicine/vet-visit-decisions/can-i-give-my-cat-melatonin) - [How to Give Your Cat Liquid Medicine Without a Syringe: Alternative Methods](/knowledge/veterinary-medicine/pet-medication-guide/give-cat-liquid-medicine-without-syringe) - [Gabapentin Dosage Calculator for Cats & Dogs: Veterinary Dosage Guide](/knowledge/veterinary-medicine/calculators-clinical-tools/gabapentin-dosage-calculator-for-cats-dogs-veterinary-dosage-guide) - [Revolution Plus for Cats: Selamectin Sarolaner Feline Dose Guide](/knowledge/veterinary-medicine/calculators-clinical-tools/revolution-plus-for-cats-selamectin-sarolaner-feline-dose-guide) - [What Human Medications Are Safe for Cats? A Vet's Guide to OTC Options](/knowledge/veterinary-medicine/vet-visit-decisions/human-medications-safe-for-cats) - [Clavamox Feline Dosage & Administration Calculator: Veterinary Dosage Guide](/knowledge/veterinary-medicine/calculators-clinical-tools/clavamox-feline-dosage-administration-calculator-veterinary-dosage-guide) - [ProZinc Insulin for Cats: Dose, Syringes, and Monitoring](/knowledge/veterinary-medicine/endocrine-diseases/prozinc-insulin-cats-dose) - [Vetsulin for Dogs: Dosing, Storage, and Owner Instructions](/knowledge/veterinary-medicine/pet-medication-guide/vetsulin-for-dogs-dosing-instructions) - [Ivermectin for Cats: Dosage, Safety and Alternatives](/knowledge/veterinary-medicine/pet-medication-guide/ivermectin-cats-dosage) ## References 1. [Efficacy and Safety of Non-Insulin Antidiabetic Drugs in Cats: A Systematic Review](https://pubmed.ncbi.nlm.nih.gov/40941356/). Animals : an open access journal from MDPI, 2025. 2. [Insulin Therapy in Small Animals, Part 2: Cats](https://pubmed.ncbi.nlm.nih.gov/36906468/). The Veterinary clinics of North America. Small animal practice, 2023. 3. [Pharmacokinetics of Bexagliflozin After Intravenous and Oral Administration in Cats](https://pubmed.ncbi.nlm.nih.gov/41964569/). Journal of veterinary pharmacology and therapeutics, 2026. 4. [To treat or not to treat: Experiences and considerations of veterinarians in management of cats with diabetes mellitus](https://pubmed.ncbi.nlm.nih.gov/41642848/). PloS one, 2026. ## Further Reading - [American Veterinary Medical Association: First Aid Tips for Pet Owners](https://www.avma.org/resources-tools/pet-owners/emergencycare/first-aid-tips-pet-owners) - [Merck Veterinary Manual: Cat Owners](https://www.merckvetmanual.com/cat-owners) - [Cornell Feline Health Center: Health Information](https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information)