Insulin brands for dogs and cats in the UK, and matching the right syringe

Quick answer

UK vets most often prescribe Caninsulin (porcine lente, licensed for dogs and cats) or ProZinc (protamine zinc, licensed for cats and dogs). Both are U-40 insulins, meaning 40 units per millilitre, and both need U-40 syringes.

Human insulins such as glargine are sometimes used off-licence in cats, and those are U-100.

The syringe must match the insulin. The number is a concentration the markings are calibrated against, not a size. Draw U-40 insulin into a U-100 syringe and the markings overstate what you have drawn, so the pet gets roughly 40% of the intended dose. Do it the other way round and they get about two and a half times too much.

Why this is the mistake worth guarding against

It is invisible. There is no sensation, no error message and nothing to see in the syringe — the fluid looks the same either way. An owner can inject confidently twice a day for months while delivering a fraction of the prescribed dose, and the only sign is a pet whose diabetes will not settle. That is why our guide to diabetes that will not stabilise lists syringe mismatch first.

It usually happens at the margins of normal life rather than through carelessness:

• Buying syringes online to save money, and ordering the common U-100 type.
• Running out at a weekend and borrowing from someone whose pet is on a different insulin.
• Switching insulin brands without the syringes being switched at the same time.
• A second carer topping up supplies from a different box.

The insulins UK owners are most likely to be given

Caninsulin (porcine lente)

Licensed for both dogs and cats, and the one most UK owners meet first. It is a suspension, so the solid and liquid separate in the vial and it must be shaken until the liquid is uniformly cloudy before each dose. Let any foam settle before drawing up. A vial that will not go evenly cloudy, or that has clumps sticking to the glass, should go back to your practice rather than into your pet.

It is supplied with U-40 syringes, or as a cartridge for the VetPen.

ProZinc (protamine zinc)

Licensed for cats and for dogs in the UK, and also U-40. Like Caninsulin it is a suspension and must be mixed before use — follow the leaflet, because mixing instructions differ between products and are not interchangeable either.

Glargine and other human insulins

Sometimes used off-licence in cats, particularly where a vet is working towards remission. These are U-100 and need U-100 syringes. If your cat moves from a veterinary insulin to one of these, the syringes change with it.

Senvelgo

Not insulin. Senvelgo is velagliflozin, an oral SGLT2 inhibitor licensed for cats in the UK. It works on the kidneys, passing glucose out in the urine, and it comes with its own rules: contraindicated in cats previously or currently treated with insulin, contraindicated in a cat in ketoacidosis, and capable of allowing ketoacidosis to develop while the glucose reading still looks fine. There is a fuller guide to oral treatment for diabetic cats.

If you have a VetPen rather than syringes

A pen is not simply a tidier syringe, and two steps catch people out:

Prime it before every injection. The pen needs an air shot to confirm insulin is flowing and to clear the needle. Skipping it means dialling a dose and delivering less than that.

Hold for a slow count of five before withdrawing. A pen delivers more slowly than a syringe plunger. Pull the needle straight out and some of the dose tracks back out through the hole, with nothing to see.

Pen needles are single-use like any other. Take the needle off after dosing rather than leaving it attached, and remember the dose window is the only confirmation you get — there is no fluid level to check against.

What to ask your vet, and write down

• Which insulin is my pet on, and is it U-40 or U-100?
• Which syringes do I use, and where do I get more?
• Shaken or rolled?
• How much can the injection time move on a bad morning?
• What do I do if I am not sure the dose went in?

Our questions for your vet page has a fuller list you can take with you.

Sources and further reading

• Caninsulin and ProZinc summaries of product characteristics, available from the VMD Product Information Database.
• AAHA Diabetes Management Guidelines for Dogs and Cats.
• 2025 iCatCare consensus guidelines on feline diabetes.

Doses, brands and syringe types are decided by the vet treating your animal. This page explains what the products are; it does not tell you what your pet should be on.