You have a vial of ProZinc in the fridge, a prescription label with a number on it, and a reasonable question: does that number match your cat's weight? So you search for a dosage chart.
There isn't one. The dose lives in the FDA-approved label, the approval paperwork behind it, and a handful of veterinary references — and not one of them does the arithmetic at each weight.
The label does give a range, and it is wide: 0.1 to 0.3 IU of insulin per pound of body weight, every 12 hours.¹ For a 12 lb cat that is somewhere between 1.2 and 3.6 IU a dose. Below: that conversion at every cat weight, why three other authorities put a newly diagnosed cat near the bottom of the band, what dose cats actually end up on, and the syringe mistake that makes the number irrelevant.
Key takeaways
- The label's range is threefold wide, so a chart built on the top of it is not a starting dose. 0.1 to 0.3 IU/lb every 12 hours is 1.2 to 3.6 IU for a 12 lb cat.¹ Merck gives 0.25 U/kg, about 1 U per cat, and says starting doses "should be conservative, not exceeding 2 U/cat".³
- The same manufacturer's UK label makes the split the US one leaves out. It gives 0.2 to 0.4 IU/kg initially and reserves up to 0.7 IU/kg for "cats previously controlled on insulin".⁵ The US label applies that logic — to dogs.¹
- The dose a cat starts on is roughly half the dose it ends on. In the pivotal 151-cat study the mean twice-daily dose climbed from 1.8 IU to 3.7 IU in 45 days.²
- The syringe can undo the number entirely. ProZinc is U-40, and the label says in capitals that any other syringe "WILL RESULT IN INCORRECT DOSING".¹ A U-100 syringe draws about 40% of the intended amount.⁸
How much ProZinc insulin does a cat get per pound?
The FDA-approved label gives an initial dose of 0.1 to 0.3 IU of insulin per pound of body weight — 0.2 to 0.7 IU/kg — every 12 hours, given concurrently with or right after a meal.¹ ProZinc is protamine zinc recombinant human insulin at 40 IU per mL.²
That is a band, not a number. The table converts it at every cat weight, alongside the two tighter figures published elsewhere for the same drug. It is arithmetic, not a recommendation.
| Cat weight | (kg) | US label: 0.1–0.3 IU/lb q12h | UK label, newly diagnosed: 0.2–0.4 IU/kg q12h | Against Merck's 2 IU/cat ceiling |
|---|---|---|---|---|
| 5 lb | 2.3 | 0.5–1.5 IU | 0.5–0.9 IU | both inside it |
| 6 lb | 2.7 | 0.6–1.8 IU | 0.5–1.1 IU | both inside it |
| 7 lb | 3.2 | 0.7–2.1 IU | 0.6–1.3 IU | US top just exceeds it |
| 8 lb | 3.6 | 0.8–2.4 IU | 0.7–1.5 IU | US top exceeds it |
| 9 lb | 4.1 | 0.9–2.7 IU | 0.8–1.6 IU | US top exceeds it |
| 10 lb | 4.5 | 1.0–3.0 IU | 0.9–1.8 IU | US top is 1.5× it |
| 11 lb | 5.0 | 1.1–3.3 IU | 1.0–2.0 IU | US top is 1.65× it |
| 12 lb | 5.4 | 1.2–3.6 IU | 1.1–2.2 IU | US top is 1.8× it |
| 14 lb | 6.4 | 1.4–4.2 IU | 1.3–2.5 IU | US top is 2.1× it |
| 16 lb | 7.3 | 1.6–4.8 IU | 1.5–2.9 IU | US top is 2.4× it |
| 18 lb | 8.2 | 1.8–5.4 IU | 1.6–3.3 IU | US top is 2.7× it |
| 20 lb | 9.1 | 2.0–6.0 IU | 1.8–3.6 IU | US top is 3.0× it |
Read the last two columns against the third. The bands start together and then separate: by 14 lb the top of the US range is more than twice the 2 IU ceiling Merck names for a conservative start.³ The arithmetic also gets rounded in practice — the UK label puts dose adjustments "between 0.5 to 1 IU insulin per injection", and the American Association of Feline Practitioners advises rounding to the nearest half unit.⁵⁴
Why isn't the top of that range a starting dose?
Because the three other authorities that publish a figure for this drug all put a newly diagnosed cat near the bottom of the band — and because the US label itself applies that same reasoning two columns over, to dogs.
Start with Merck. Its chapter on diabetes mellitus in dogs and cats gives protamine zinc insulin a starting dosage of "0.25 U/kg [1 U/cat], SC, every 12 hours", then adds two conditions the charts drop: "Estimated ideal body weight, not actual weight, is used to calculate insulin dosages; starting doses should be conservative, not exceeding 2 U/cat."³ Both halves matter. Most cats who reach a diabetes diagnosis are carrying extra weight, so dosing off the scale reading inflates the result twice over.
Then the same product's UK label, which splits the range the US one presents flat: "The initial recommended dose is 0.2 to 0.4 IU insulin/kg bodyweight every 12 hours", and separately, "For cats previously controlled on insulin, a higher starting dose up to 0.7 IU insulin/kg bodyweight may be appropriate."⁵ So 0.7 IU/kg — the figure a per-pound chart reaches for as the top of its range — is, on the other side of the Atlantic, a transfer dose rather than an opening one.
Here is the part that settles it: the US label does draw that distinction — in its dog section. "The recommended starting dose for naïve dogs is the lower end of the dose range. The recommended starting dose for dogs with poorly controlled diabetes mellitus and transitioning from another insulin product is the mid to higher end of the dose range."¹ The principle is on the label; it just isn't in the cat paragraph.
And the trial behind the approval capped it anyway. Cats in the pivotal study started on 0.1 to 0.3 IU/lb "with a maximum starting dose of 3 IU every 12 hours", and the mean starting dose was 1.8 IU.² Those cats averaged 12.2 lb, so 1.8 IU is about 0.33 IU/kg — mid-range on the UK band, nowhere near the US top.
What dose do cats actually end up on?
Roughly double what they start on. In the 45-day study the mean twice-daily dose rose from 1.8 IU on day 0 to 2.6, then 3.3, then 3.6, and 3.7 IU by day 45; in the extended-use study it reached 3.8 IU by day 102.² No chart publishes this figure, and it is the one that tells you what the next two months look like.
Two independent datasets agree on where that climb lands. The trial's day-45 cats averaged 13.1 lb, so 3.7 IU is about 0.62 IU/kg.² The AAFP's feline diabetes toolkit, drawing on the ISFM guidelines, lists the median maintenance dose for ProZinc as 0.6 U/kg every 12 hours.⁴ Those two numbers come from completely different places and differ by about 4%.
Which reframes the range: 0.2 IU/kg is roughly where cats begin,⁵ 0.6 to 0.7 IU/kg where they arrive.⁴ A chart handing a newly diagnosed cat the top of the band isn't being generous. It is skipping the titration.
Why does the syringe matter as much as the number?
Because the dose is a volume, and the marks on the barrel only mean what the label says if the concentrations match. ProZinc holds 40 IU per mL, and the FDA-approved label carries the warning in capitals: "USE OF A SYRINGE OTHER THAN A U-40 SYRINGE WILL RESULT IN INCORRECT DOSING."¹ The UK label is just as flat: "A U-40 syringe must be used."⁵
A U-100 syringe is calibrated for 100 IU per mL, so the same numbered mark holds a different volume. Tufts Veterinary Emergency Treatment and Specialties quantifies both directions: a U-100 syringe with a U-40 insulin draws "only 40% of the intended amount", and a U-40 syringe with a U-100 insulin delivers "2.5 times the intended dose" — 5 units intended becoming 2 given, or 12.5.⁸
So buy syringes to match the insulin, not the last box. Tufts notes U-100 syringes carry an orange cap and U-40 syringes a red one, and that half-unit markings exist for the small doses cats need.⁸ Never assume two vials in the same fridge take the same barrel: glargine and detemir are U-100, ProZinc and Vetsulin U-40.⁴⁸
Handling matters too, because an unmixed suspension is an inaccurate dose. "DO NOT SHAKE OR AGITATE THE VIAL": ProZinc is mixed by gently rolling it before each dose, stored upright and refrigerated, and not used if clumps or white particles persist.¹
⚠️ What if your cat didn't eat, or you aren't sure the injection went in?
Both have a published answer, and neither is "give it anyway and see".
On food: the label ties the dose to the meal, "concurrently with or right after a meal".¹ VCA Animal Hospitals gives the reasoning and the fallback — your cat should eat first, because "once the insulin is administered, it cannot be removed from the body"; if only half the food is eaten, give only a half dose, and if that happens more than once the cat needs to be seen. Then the line worth keeping: "it is always better in the short term for blood sugar to be too high than too low."⁶
ProZinc's own extended-use study shows how serious that is. Fourteen cats died or were euthanized during it, and in two of those cases "continued use of insulin despite anorexia and signs of hypoglycemia contributed to the deaths".¹ A cat who has stopped eating is a phone call, not a judgement call.
On a dose you aren't sure about: do not repeat it. VCA covers the fumbled injection directly — "If you are unsure if you administered it correctly, or if you 'missed,' do not administer additional insulin. Simply resume your normal schedule and give the next insulin injection at the regular time."⁶ Wet fur afterwards is the tell that it went onto the coat rather than under it.⁶ Write it down; that note is what your vet needs at the recheck. The same reasoning for the other species is in what happens if you forgot to give your dog insulin.
How do you tell whether the dose is working?
By a glucose nadir and a set of clinical signs, on a schedule — not by how the cat seems on any one day. The label's own definition: control counted as adequate when "the glucose nadir from a 9-hour blood glucose curve was between 80 and 150 mg/dL" and polyuria, polydipsia and weight loss had improved.¹
The AAFP's standard protocol turns that into a routine: a recheck 5 to 10 days after starting, a glucose curve run at home rather than the clinic, adjustments in 0.5 U increments, then an exam plus curve every 5 to 7 days until stable. Its targets are a nadir above 80 mg/dL, a peak below 300, and glucose under 250 for most of the day without hypoglycemia.⁴
On how fast to move, the sources differ, and both numbers are worth knowing. The AAFP's intensive protocol says the dose "should not be increased more frequently than q3 days"; Merck says dosages "should not be increased more often than every 1–2 weeks"; the UK label says an increase should "in general" wait about a week, because full insulin action needs an equilibration phase.⁴³⁵ All three point the same way: slower than instinct suggests.
What you can contribute is the record. Merck notes that at-home monitoring "improves glycemic control in both species and increases the likelihood of obtaining remission in cats".³ Water intake, litter-box output, appetite, weight and the dose and time of every injection are the inputs behind each adjustment — the discipline described in tracking insulin shots day to day. Not yet diagnosed? The symptoms to look for in a cat come first.
⚠️ What are the signs that a cat has had too much insulin?
Low blood sugar, and it moves fast. VCA puts hypoglycemia below 40 mg/dL at "life-threatening", with the risk peaking 5 to 8 hours after an injection.⁶ ProZinc's label is blunter: "Overdose can result in profound hypoglycemia and death", and hypoglycemia has occurred "even at established doses".¹
In the 45-day field study, 71 of 176 cats recorded a blood glucose below 50 mg/dL at some point. Most had no clinical signs; where signs appeared they were "lethargic, sluggish, weak, trembling, uncoordinated, groggy, glassy-eyed or dazed", and 17 cats were given oral glucose or food. One cat had a serious event with stupor, lateral recumbency, hypothermia and seizures, and recovered.¹
What you are watching for: weakness and lethargy, shaking, unsteadiness, a "drunken" walk, or a cat who seems sedated when you call them — then four words, "Low blood sugar is a medical emergency!"⁷ Cats sleep a lot anyway, so the mild version is easy to miss.⁶
- Take a glucose reading if you have a meter, and call. Note the dose and the clock time of the last injection.
- Offer food if your cat can swallow safely. Your vet may ask for an extra meal and a recheck shortly after.⁶
- If your cat is seizing or unconscious, go now. VCA notes a sugar syrup such as maple or corn syrup can be applied to the gums on the way, and that severe hypoglycemia is reversed with intravenous glucose.⁶
- Do not give the next dose to get back on schedule. The label says to withhold insulin temporarily and adjust if indicated — the vet's call.¹ In the US, ASPCA Animal Poison Control is on 888-426-4435, 24 hours a day, 365 days a year; a fee may apply.⁹
Why do two-person households double-dose insulin?
Because insulin is given twice a day, around meals, by whoever is in the kitchen — exactly the shape of task two people both complete. VCA names the mechanism and the fix in one breath: too much insulin "can occur because the insulin was not properly measured in the syringe or because two doses were given. Place a chart in a central location to record insulin administration and prevent the cat being treated twice."⁶
Not a louder reminder, and not one person taking charge: a shared record both people write to and both can read. A reminder tells you a dose is due; only a record tells you whether it has already been given. That distinction is the argument avoiding double-dosing pet medication makes at length, and insulin is where it matters most — a doubled dose cannot be taken back out.
Veterinary medical disclaimer: SteadyTails is a logging and coordination tool, not a substitute for veterinary care. Nothing here is a diagnosis, a prescription or a dosing instruction. ProZinc is prescription-only, and every figure quoted or derived on this page is a label range, a published reference rate or a field-study mean — not an amount to give your cat. The only dose that governs your cat is the one your veterinarian wrote on the label. Do not start, stop, repeat, skip or adjust an insulin dose on your own judgement, and never use a syringe that does not match the concentration in the vial. If your cat has stopped eating, is weak, wobbly, unresponsive, trembling or seizing, contact your veterinarian or an emergency animal hospital immediately.
"Did she get her 7pm insulin? And did she actually eat first?"
Insulin is the drug where a shared record beats a reminder: a doubled dose cannot be undone, and a skipped meal changes the dose. SteadyTails keeps every injection, unit count, time and skipped dose on one timeline the whole household writes to, with meals and daily wellbeing ratings laid over it — so the glucose curve your vet reads has a story next to it. Available now on the App Store • Android coming soon.
Download on the App Store →References
- U.S. Food and Drug Administration / DailyMed. PROZINC — protamine zinc recombinant human insulin injection, suspension, Boehringer Ingelheim Vetmedica, Inc. — cat dosage: "The initial recommended PROZINC dose is 0.1 - 0.3 IU insulin/pound of body weight (0.2 - 0.7 IU/kg) every 12 hours. The dose should be given concurrently with or right after a meal"; "USE OF A SYRINGE OTHER THAN A U-40 SYRINGE WILL RESULT IN INCORRECT DOSING"; "DO NOT SHAKE OR AGITATE THE VIAL"; "PROZINC should be mixed by gently rolling the vial prior to withdrawing each dose from the vial"; "do not use the product if clumps or visible white particles persist after gently rolling the vial"; "Using a U-40 insulin syringe, the injection should be administered subcutaneously on the back of the neck or on the side of the cat"; glycemic control "considered adequate if the glucose nadir from a 9-hour blood glucose curve was between 80 and 150 mg/dL and clinical signs of hyperglycemia such as polyuria, polydipsia, and weight loss were improved"; dog section: "The recommended starting dose for naïve dogs is the lower end of the dose range. The recommended starting dose for dogs with poorly controlled diabetes mellitus and transitioning from another insulin product is the mid to higher end of the dose range"; precautions: "Overdose can result in profound hypoglycemia and death"; "Use of this product, even at established doses, has been associated with hypoglycemia… Insulin should be temporarily withheld and, if indicated, the dosage adjusted"; adverse reactions: "Hypoglycemia (defined as a blood glucose value of < 50 mg/dL) occurred in 71 of the cats", signs "described as lethargic, sluggish, weak, trembling, uncoordinated, groggy, glassy-eyed or dazed", "In 17 cases, the veterinarian provided oral glucose supplementation or food as treatment", "One cat had a serious hypoglycemic event associated with stupor, lateral recumbency, hypothermia and seizures"; extended use: "Fourteen cats died or were euthanized during the extended use study. In two cases, continued use of insulin despite anorexia and signs of hypoglycemia contributed to the deaths"; storage: "Store in an upright position under refrigeration at 36-46°F (2-8°C). Do not freeze. Protect from light." dailymed.nlm.nih.gov Retrieved 2026-10-04.
- U.S. Food and Drug Administration, Center for Veterinary Medicine. Freedom of Information Summary, NADA 141-297 (PROZINC), date of approval October 28, 2009 — amount of active ingredient "40 international units (IU) insulin/mL"; "How Supplied: 10 mL multidose vials"; "PROZINC should be administered subcutaneously along the back of the neck or on the side of the cat using a U-40 insulin syringe"; field study: "The starting dose of PROZINC was 0.1 – 0.3 IU/lb (0.2 – 0.7 IU/kg) every 12 hours with a maximum starting dose of 3 IU every 12 hours"; "Of the 151 cats included in the effectiveness analysis, 115 (76.2%) were considered treatment successes. The 90% confidence interval was 70.5% to 81.9%"; Table 1 mean body weight 12.2 lbs on Day 0 and 13.1 lbs on Day 45; Table 4 "Mean insulin dose given twice daily" — Day 0: 1.8 IU (range 0.5, 3.0); Day 7: 2.6 (1.0, 5.0); Day 14: 3.3 (1.0, 7.0); Day 30: 3.6 (0.0, 9.0); Day 45: 3.7 (0.5, 10); Table 6 extended use — Day 45: 3.7 IU; Day 68: 3.7; Day 102: 3.8. animaldrugsatfda.fda.gov Retrieved 2026-10-04.
- Merck Veterinary Manual. Diabetes Mellitus in Dogs and Cats — "For cats with newly diagnosed diabetes, protamine zinc insulin (PZI; starting dosage 0.25 U/kg [1 U/cat], SC, every 12 hours) and insulin glargine (starting dosage 0.25–0.5 U/kg [1–2 U/cat], SC, every 12 hours) are the most common insulins used"; "They produce comparable glycemic control and remission rates"; "Estimated ideal body weight, not actual weight, is used to calculate insulin dosages; starting doses should be conservative, not exceeding 2 U/cat. Cats should be reevaluated 5–7 days after starting treatment before adjustments are made to the insulin dosage, unless hypoglycemia develops. Insulin dosages should not be increased more often than every 1–2 weeks"; "Long-acting insulins (glargine or protamine zinc insulin [PZI]) are preferred for cats"; "Studies in both dogs and cats have shown that at-home monitoring of diabetes mellitus improves glycemic control in both species and increases the likelihood of obtaining remission in cats." merckvetmanual.com Retrieved 2026-10-04.
- American Association of Feline Practitioners. Diabetes Educational Toolkit — Treatment, table compiled from the ISFM Guidelines on Diabetes Mellitus — "PZI (Prozinc) U40 Long-acting (13-24 hours) 0.2-0.7 U/kg q12h 0.1-0.3 U/lb q12h 0.6 U/kg q12h" (type, concentration, duration, starting dose and median maintenance dose respectively); "Glargine (Lantus) U100… 2.5 U/cat q12h"; "Detemir (Levemir) U100… 1.75 U/cat q12h"; "Dosing initiated at 0.25-0.5 U/kg q12h (Most average cats are initiated on 1 U/cat q12 hrs. Round to the nearest half unit if more precision is required.)"; "Adjustments are usually made in 0.5 U increments"; "Insulin dose should not be increased more frequently than q3 days"; standard protocol — "Recheck examination in clinic 5-10 days after starting insulin", "BG curve… Performed at home the day before examination (preferred)", "Patient examination + BG curve (home or clinic) q5-7 days until stable, then q3-6 months", goals "BG nadir >80 mg/dl", "BG peak <300 mg/dl", "BG <250 mg/dl… for most of the day without hypoglycemia"; "Low carb diet <12% metabolizable energy (ME)"; the dose table carries the note "This table was created based on the ISFM Guidelines on Diabetes Mellitus". catvets.com Retrieved 2026-10-04.
- NOAH Compendium of Animal Medicines. ProZinc 40 IU/ml suspension for injection for cats and dogs — Dosage and administration (UK summary of product characteristics, Boehringer Ingelheim) — cats: "The initial recommended dose is 0.2 to 0.4 IU insulin/kg bodyweight every 12 hours"; "For cats previously controlled on insulin, a higher starting dose up to 0.7 IU insulin/kg bodyweight may be appropriate"; "Adjustments of insulin dose if required should usually be done between 0.5 to 1 IU insulin per injection"; "Any dose adjustment (i.e. increase of dose) should be in general performed after several days (e.g. 1 week) since full action of insulin requires an equilibration phase. Dose reductions due to observed hypoglycaemia or suspected Somogyi effect (rebound hyperglycaemia) may be of 50% or higher"; "A U-40 syringe must be used"; "The suspension should be mixed by gently rolling the vial prior to withdrawing each dose from the vial"; "The dose should be given concurrently with or immediately after a meal." noahcompendium.co.uk Retrieved 2026-10-04.
- VCA Animal Hospitals. Diabetes Mellitus in Cats — Insulin Treatment — "It is important to make sure you match the insulin concentration with the proper insulin needles… There are two common forms of insulin and corresponding syringes: U-100 and U-40"; "Insulin is a suspension not a solution, so before administering it you must mix it. Some insulins should be gently rolled and not shaken"; "If you are unsure if you administered it correctly, or if you 'missed,' do not administer additional insulin. Simply resume your normal schedule and give the next insulin injection at the regular time"; "Alcohol makes the skin or hair wet, so you can't see if you have accidentally injected insulin onto the surface of the skin"; "If the blood sugar falls below 40 mg/dl (2.2 mmol/L), it can be life-threatening"; "Your cat should eat before you give an insulin injection, because once the insulin is administered, it cannot be removed from the body. If your cat does not eat, or if only half of the food is eaten, give only a half half-dose of insulin. If this happens more than once, take your cat to the veterinarian for assessment. Remember that it is always better in the short term for blood sugar to be too high than too low"; "This can occur because the insulin was not properly measured in the syringe or because two doses were given. Place a chart in a central location to record insulin administration and prevent the cat being treated twice"; "A cat is most likely to become hypoglycemic at the time of peak insulin effect: 5–8 hours after an insulin injection"; "Since many cats sleep a lot during the day, this important sign is easily missed"; "Your veterinarian may have you offer an extra meal and recheck the glucose level a short time after your cat eats"; "This emergency can only be reversed with intravenous administration of glucose… A sugar syrup, such as maple syrup or corn syrup, can be applied to the gums as you are getting your cat to the veterinarian." vcahospitals.com Retrieved 2026-10-04.
- VCA Animal Hospitals. Diabetes Mellitus in Cats — Overview — "If a cat receives too much insulin, it is possible for the blood sugar level to drop dangerously low (hypoglycemia). For this reason, it is important to be very careful to ensure the cat receives the correct dose of insulin"; "Clinical signs displayed by a cat with a very low blood sugar level include weakness and lethargy, shaking, unsteadiness and even convulsions"; "In mild cases of hypoglycemia, you may observe wobbling or a 'drunken' walk, or the cat may seem sedated when you call or pet them. Low blood sugar is a medical emergency!" vcahospitals.com Retrieved 2026-10-04.
- Tufts Veterinary Emergency Treatment & Specialties. Understanding Insulin for Diabetic Pets — "A U-100 syringe is calibrated for 100 units per mL. If you accidentally use this syringe with U-40 insulin, you'll underdose your pet—drawing only 40% of the intended amount"; "A U-40 syringe, when used with U-100 insulin, will overdose your pet—delivering 2.5 times the intended dose"; "If your pet is prescribed 5 units of a U-40 insulin, but you accidentally draw it up using a U-100 syringe, you will only give 2 units of insulin—not enough to control blood sugar. If reversed, you could give 12.5 units instead of 5—a potentially life-threatening overdose"; "make sure the concentration matches the insulin (U-100 for Humulin N, Lantus; U-40 for ProZinc, Vetsulin)… U-100 syringes have an orange cap and U-40 syringes have a red cap"; "You should never use a non-insulin syringe to administer insulin"; "There are syringes with 1/2 unit markings if your pet requires very small or precise doses (common in cats and small dogs)"; "Most insulin products should be kept in the refrigerator, ideally between 36°F and 46°F (2°C and 8°C). Avoid freezing"; "Humulin N, Lantus, and ProZinc should be gently rolled between your hands before use" tuftsvets.org Retrieved 2026-10-04.
- ASPCA. Animal Poison Control Center — "(888) 426-4435"; "ASPCA Poison Control is your best resource for any animal poison-related emergency, 24 hours a day, 365 days a year"; "A consultation fee may apply." aspca.org Retrieved 2026-10-04.
