How much bute for a horse?

Bute is prescription-only and this is a reference tool, not a prescription — your vet sets both the dose and the length of the course. What it adds to a dosage chart is the one input none of them ask for: how many days in a row, because the safe amount falls the longer a course runs.

lb

An average adult riding horse is about 1,100 lb (500 kg).

Why?Guess this high and you overdose the horse. Every published dose is milligrams per kilogram, so a 200 lb error moves the answer by nearly a gram a day, and weight is the one input on this form that is worth measuring rather than estimating.

Don't know it? Work it out from a tape measure

How many consecutive days the horse will be on it.

Why?This is the input no dosage chart asks for, and it changes the answer. The published definition of an overdose is a dose and a duration together, so a rate that is fine for three days becomes an overdose at nine.

The daily amount is the same either way; this only splits it.

Why?The veterinary monograph doses horses every twelve hours. Splitting the day's amount in two keeps the peak lower without changing the total, which is why it is the usual instruction.

All three deliver a gram a unit, so the count is the same.

Why?A syringe marking, a level scoop of powder and one horse-sized tablet each hold one gram of phenylbutazone. That is a genuine convenience and it is the reason bute dosing can be done in your head once you know the gram figure.

Read it off your own label if it differs.

Why?Tablets are also sold at 100 mg and 200 mg, mostly for small animals, and a bottle of those is easy to mistake for the horse-sized ones. Check the strength on the bottle before you count anything out.

A syringe holds 20 g; a jar or a bottle holds 100 g.

Why?Taken from the FDA packaging records rather than a retailer's listing. It is here so the tool can tell you how long what you have in the cupboard will actually last.
Phenylbutazone a day—The published range for a horse this size, already trimmed to what is safe for the number of days you entered. The top of the range is a first-day dose and buys no extra pain relief.
Per dose—
Why?The day's amount split across the doses you give. Mixing this up with the daily figure is the commonest way a horse gets twice what it should.
Syringe markings per dose—
Why?Each marked step on the plunger is one gram, which on the labelled syringe is 3 mL.
Level scoops per dose—
Why?Using the scoop that came in the jar, levelled off. A heaped scoop is not a measurement.
Tablets per dose—
Why?Horse tablets are one gram each, so this is usually a whole number or a clean half.
Dose rate—
Why?What that works out at per kilogram, which is the unit every study and every rule is written in.
Never more than, in any one day—
Why?The lower of the weight-based maximum and the flat four grams a day the label allows any horse. It is a hard ceiling for a single day and does not rise for a longer course.
One full pack lasts—
Why?At the daily amounts above, so the long figure is the low dose and the short one the high dose.

Bute is a prescription medicine. This page sets out what the published dosing evidence says and does the arithmetic on it.

It is not a prescription, and the decision to treat, at what dose and for how long, is your vet’s.

How much bute for a horse?

For an average 1,100 lb (499 kg) riding horse, the standard dose is 2.2 g of phenylbutazone a day, usually split into 1.1 g morning and evening.

On the first day of a course that can go as high as 4 g, and for a long-running course it drops to 1.1 g a day.

That is the whole answer in grams, and grams is the useful unit here: one syringe marking, one level scoop of powder and one horse-sized tablet each hold 1 g of phenylbutazone.

The dose everyone quotes is a ceiling, not a target

The number most often repeated is 8.8 mg/kg a day, which is 4 g for a 1,000 lb (454 kg) horse. It is the top of the label range, and it is the least useful figure on this page.

A person lifting and holding a horse’s front hoof to inspect the sole
Most bute is given for a musculoskeletal problem, which is what the FDA label approves it for. The dose is the same whatever the cause; what changes is how long the course needs to run. Photo: Pixabay

Here is why. In the published comparison, running horses at 8.8 mg/kg a day instead of 4.4 gave lame horses no additional pain relief at all.

The review’s own conclusion is blunt: exceeding the recommended dose “only increases the risk of toxicity with no analgesic benefit”.

So the top of the range costs you risk and buys you nothing. It is a first-day dose to get ahead of a problem, not a rate to sit on.

Bute for horses dosage chart

Every row below is the calculator above, run at that weight. It is generated from the same code, so the chart and the tool cannot drift apart.

Bute for horses dosage chart, generated by the calculator above. Every figure is grams of phenylbutazone, which is one syringe marking, one level scoop or one horse tablet a gram.
Horse Body weight Standard, a day Each of two doses Most in one day Past a week, a day
Miniature 250 lb (113 kg) 0.5 g 0.2 g 1 g 0.2 g
Small pony 400 lb (181 kg) 0.8 g 0.4 g 1.6 g 0.4 g
Large pony 700 lb (318 kg) 1.4 g 0.7 g 2.8 g 0.7 g
Small horse 900 lb (408 kg) 1.8 g 0.9 g 3.6 g 0.9 g
Riding horse, 500 kg 1,102 lb (500 kg) 2.2 g 1.1 g 4 g 1.1 g
Riding horse, 600 kg 1,323 lb (600 kg) 2.6 g 1.3 g 4 g 1.3 g
Warmblood 1,350 lb (612 kg) 2.7 g 1.3 g 4 g 1.3 g
Draft 1,800 lb (816 kg) 3.6 g 1.8 g 4 g 1.8 g

The last two columns are the ones no other chart carries. A dose that is correct on day one is an overdose by day nine, and that is a published definition rather than a caution.

How many days in a row can you give a horse bute?

This is the question that decides whether a dose is safe, and no dosage chart online asks it.

The 2023 case series that defined an NSAID overdose in horses did not define it as an amount. It defined it as an amount and a length of time, in three parts.

More than 8.8 mg/kg in a single day is an overdose.

So is more than 4.4 mg/kg a day for more than four days, and so is more than 2.2 mg/kg a day for more than eight consecutive days.

Read that as a ceiling that falls as the course runs on, which is exactly how the calculator applies it.

What the published overdose definition allows, by how long the course runs
Days in a row Highest rate that stays inside it A 1,100 lb (499 kg) horse
1 8.8 mg/kg a day 4 g
4 8.8 mg/kg a day 4 g
5 4.4 mg/kg a day 2.2 g
8 4.4 mg/kg a day 2.2 g
9 2.2 mg/kg a day 1.1 g
14 2.2 mg/kg a day 1.1 g

In those 35 cases the median horse had been on bute for nine days before right dorsal colitis was diagnosed, and the condition killed 43% of them.

The honest caveat belongs here too, from the same paper: four of the 25 horses whose dosing was known developed the disease on recommended doses. An overdose is not a prerequisite.

Where the dose comes from

What makes these figures worth trusting is not any one source. It is that a drug label, a pharmacology monograph, two clinical studies forty years apart and a competition rulebook all land in the same place.

Three independent sources, one dose envelope
Source What it says In mg/kg a day
FDA labels — paste, powder and tablets “1 to 2 g of phenylbutazone per 500 lb. (227 kg) of body weight daily. Do not exceed 4 g daily.” 4.4 to 8.8
USP veterinary monograph “4.4 mg per kg of body weight every twelve hours initially, followed by 2.2 mg per kg every twelve hours.” 8.8, then 4.4
Collins & Tyler 1984, 269 horses “less than or equal to 8.8 mg/kg of body weight/day for less than or equal to 4 days … remained clinically normal.” 8.8 for up to 4 days
Flood 2023, 35 colitis cases Overdose is “more than 4.4 mg/kg … for more than 4 days, or more than 2.2 mg/kg for more than 8 consecutive days”. 4.4 past 4 days, 2.2 past 8
Equestrian Canada, competition “not more than 4.4 milligrams per kilogram … for not more than five consecutive days.” 4.4

Note what Collins & Tyler and Flood found independently: the same 8.8 mg/kg line and the same four-day boundary, one from 269 treated horses in 1984 and one from colitis cases in 2023.

The two disagree in one place and we take the stricter reading.

Collins & Tyler found 2 to 4 mg/kg a day safe for up to 50 days; Flood counts anything above 2.2 mg/kg past eight days as an overdose.

How much bute for a 1000 lb horse?

2 g a day at the standard rate, or 1 g twice a day. On the first day up to 4 g.

A 1,000 lb (454 kg) horse is the animal the label was written around, and it shows: 8.8 mg/kg comes to almost exactly the 4 g a day that the label sets as a flat ceiling for any horse.

That coincidence has a consequence nobody mentions.

Past 1,002 lb (455 kg) the flat 4 g cap runs out before the weight-based figure does, so a 1,500 lb (680 kg) horse held to the label maximum is on 5.9 mg/kg, not 8.8.

How much bute for a 600kg horse?

2.6 g a day, split as 1.3 g twice, for a horse of 600 kg (1,323 lb).

The single-day maximum for a horse that size is 4 g, which is the flat label cap rather than the milligrams-per-kilogram figure.

How much bute for a pony?

Arithmetically a pony is just a smaller horse: a 700 lb (318 kg) pony gets 1.4 g a day at the standard rate, or 0.7 g twice.

Clinically it is not that simple, and this is the one place where the mathematics understates the risk.

Ponies are reported to be more susceptible to these drugs than full-sized horses. In the study that established it, ten mg/kg a day for one to two weeks made seven of eight ponies ill and killed three of them.

Ten mg/kg is barely above the 8.8 mg/kg the label allows as a maximum. Below 800 lb (363 kg) the calculator says so on the result.

Paste, powder or tablets

The three horse formulations are unusually easy to work with, because they converge on the same unit. A syringe marking, a level scoop and one tablet each deliver 1 g.

What differs is how much you get and how easily you can measure a part of a dose.

What each formulation holds, from the FDA packaging records
Formulation One unit is A full pack holds Days for a 1,100 lb horse
Paste syringe 1 g per marking, 3 mL 20 g 9
Powder with a scoop 1 g per level scoop 100 g 45
Tablets 1 g per tablet 100 g 45

Two things to watch. Tablets are also sold at 100 mg and 200 mg for small animals, and a bottle of those looks much like a bottle of the horse-sized ones.

And the scoop is the one that comes in the jar, levelled off. A heaped scoop is not a measurement, and the label is explicit about “level scoops”.

Powder on feed absorbs more slowly than you think

The USP monograph is direct about it: “feed, especially hay, delays time to peak effect and decreases peak plasma concentrations”.

The published time to peak in a fed horse is 12 to 14 hours, against a plasma half-life of 4 to 6 hours. Roughly 70% of an oral dose reaches the bloodstream at all.

None of that makes powder a bad choice. It does mean a dose mixed into a feed in front of a full hay net is not working on the timetable the label implies.

Who is at more risk

Ponies and small horses. More susceptible than full-sized horses, and the group in which the classic toxicity study recorded deaths.

A rider crouching to fasten protective boots onto a bay horse’s front legs in a yard
Bute masks the sign as well as the pain, so a horse on it needs looking at more often rather than less. Photo: Pexels

Foals. Slower clearance and a longer half-life than adults, more body water and lower plasma protein.

They should be dosed lower, not simply scaled down.

Any horse that is dry, sick or old. Dehydration, kidney disease, liver disease and sepsis all reduce the perfusion and elimination that keep the drug safe.

Older horses clear it more slowly, so the same dose reaches a higher level.

A horse already on another anti-inflammatory.

Giving two NSAIDs at recommended doses is the equivalent of a double dose of one, and that is not an analogy — it is what the review says the additive effect amounts to.

Merck’s manual adds the caveat that governs all of it: toxicosis “can occur at lower than recommended dosages in some patients”. A correct dose is not a guarantee, which is why the horse is watched and not just measured.

Common questions about bute dosage

Can you give too much bute to a horse?

Yes, and the margin is narrower than most owners think.

The largest review of the subject calls the safety margin of these drugs narrow, and in the case series behind the duration rule above, right dorsal colitis killed 43% of the horses that developed it.

What makes bute unusual is that it does not clear in proportion to the dose: the monograph notes it “follows zero-order (dose-dependent) kinetics” in horses, so a bigger dose stays in the blood disproportionately longer.

How much bute do you give a horse per day?

For an 1,100 lb (499 kg) horse, 2.2 g a day is the standard rate, usually split as 1.1 g twice.

The most any horse may have in one day is 4 g, and past four days in a row the published ceiling falls to 4.4 mg/kg a day.

How much phenylbutazone to give a horse?

Phenylbutazone is bute — the same drug, and the same figures.

The published rate is 4.4 mg/kg twice on the first day and 2.2 mg/kg twice after that, which for a 1,000 lb (454 kg) horse is 2 g a day.

Does bute bring down swelling in horses?

It does. Phenylbutazone is a non-steroidal anti-inflammatory, so it is working on the inflammation as well as the pain, and it brings a temperature down too.

That is also why it is not a drug to give and then forget: it can mask the sign that would have told you something was getting worse.

How long does it take for bute paste to kick in?

Longer than most people assume, and it depends on what the horse is eating.

The published time to peak in a fed horse is 12 to 14 hours, because the monograph finds that “feed, especially hay, delays time to peak effect and decreases peak plasma concentrations”.

Giving it to a horse standing at a full hay net is the slow way.

Which is better, Banamine or bute?

Neither, in general — they are chosen for different jobs. For orthopaedic pain the published comparison found phenylbutazone and flunixin gave comparable analgesia over four days, while flunixin is the usual choice for colic.

What matters far more is that you never give both: two NSAIDs at recommended doses is the equivalent of a double dose of one.

Where can you buy bute?

From a veterinarian, and only from one. Every FDA label carries the same line: federal law restricts this drug to use by or on the order of a licensed veterinarian.

That is why a dosage tool can tell you what the arithmetic says and cannot tell you whether to give it.

How much bute for a horse in kg of body weight?

The dose is written per kilogram in the first place: 2.2 to 8.8 mg per kilogram a day depending on the day of the course. A 500 kg horse is 2.2 g a day at the standard rate, and a 600 kg horse 2.6 g.

Can you give bute before a competition?

Under most rulebooks yes, within limits, but they are stricter than the label.

Equestrian Canada’s guidance is 4.4 mg/kg a day, given at least 12 hours before competing and for no more than five days running, and USEF tests to a plasma limit of 15 micrograms per millilitre.

Neither permits a second anti-inflammatory alongside it.

Where these figures come from