Insulin Dosing for Dogs and Cats

The mistake that matters most: U-40 versus U-100

Before any dose discussion, there is a concentration problem that causes real harm in veterinary practice, and it has nothing to do with the arithmetic.

Vetsulin and Caninsulin — the porcine lente insulins licensed for dogs and cats — are U-40, meaning 40 units per millilitre. Human insulins such as glargine, and most syringes sold in pharmacies, are U-100: 100 units per millilitre. The syringe barrel is printed for one concentration only.

The second row explains the frustrating case: a dog that never seems to respond, on a dose that keeps being raised. The fourth row is the dangerous one. Either way the fix is the same — read the concentration printed on the vial and match the syringe to it, every time, including when a pharmacy substitutes a product or you switch brands. Our units-to-mL converter shows exactly how the volumes differ.

Starting doses for dogs

The AAHA task force recommends lente insulin (Vetsulin) as first choice for dogs, at a starting dose of 0.25 units per kg every 12 hours, rounded to the nearest whole unit. The product label itself quotes a starting figure of 0.5 IU/kg, so both numbers appear in practice and your vet will choose based on the individual animal.

Where dogs end up is a different question from where they start. Most well-controlled dogs sit around an average of 0.5 units per kg twice daily, within a range of roughly 0.2 to 1.0 u/kg. That spread is wide because it reflects real biological variation, not imprecision — which is why the dose is titrated against blood glucose curves rather than calculated once and left alone.

Figures rounded to whole units as the guideline directs. The dog insulin calculator works these out for any weight.

Cats are dosed differently — and this surprises people

The starting dose for a diabetic cat is 1 unit per cat every 12 hours. Not per kilogram — per cat.

The guideline is explicit that even a very large cat should not start above 2 units per cat every 12 hours. This is the opposite of the intuition most owners bring from human or canine dosing, where weight drives everything. For cats the starting dose is deliberately flat and conservative, because feline insulin sensitivity varies enormously and the consequences of starting too high are severe in an animal this small.

Weight-based figures do appear later: most well-regulated cats settle around an average of 0.5 u/kg twice daily, within a range of about 0.2–0.8 u/kg. But that is a description of where cats end up after titration, not a starting calculation.

Two further points specific to cats. Glargine (U-100) and protamine zinc insulin remain the common choices rather than lente. And cats — unlike dogs — can go into diabetic remission, sometimes within weeks of good control. A cat in remission that continues on its previous dose is at direct risk of hypoglycemia, which is why feline cases need rechecking rather than settling.

Which insulins are used

These are not interchangeable unit for unit. They differ in onset, peak and duration as well as concentration, so switching product is a veterinary decision with a new titration, not a straight swap.

Why the dose is set by curves, not calculators

A starting dose is a place to begin. What determines the maintenance dose is a blood glucose curve — readings taken across a dosing interval to show the nadir, the duration of effect and whether the insulin is lasting the full twelve hours.

This matters because the same dose can fail in two opposite ways that look similar from the outside. Too little insulin leaves glucose high throughout. Too much can cause a rebound, where a low is followed by a counter-regulatory rise, and the owner sees a high reading and assumes more insulin is needed. Only a curve distinguishes them, which is why raising the dose in response to a single high reading is exactly the wrong move.

Watch for hypoglycemia between visits: weakness, wobbliness, disorientation, unusual quietness, tremors or seizures. Have a glucose source available and know your emergency vet’s number before you need it.

Limitations & Safety Notes

• These are published starting ranges, not prescriptions. Individual requirement varies widely and must be titrated by a veterinarian using blood glucose curves.
• Mismatching U-40 insulin with a U-100 syringe (or the reverse) is a documented cause of serious dosing error. Match the syringe to the concentration on the vial every time.
• Vetsulin/Caninsulin, PZI, glargine and NPH are not interchangeable unit for unit — they differ in concentration, onset, peak and duration.
• Cats can enter diabetic remission. Continuing a previous dose after remission causes hypoglycemia, so feline cases need regular reassessment.
• Never raise a pet’s dose in response to a single high reading. Rebound after a low looks identical to underdosing without a glucose curve.

Frequently Asked Questions