Equine Medication Calculator
Calculate drug dosages for common equine medications based on horse weight, drug type, and administration route.
About this calculator
This calculator estimates a single-dose amount for four commonly prescribed equine medications -- phenylbutazone (Bute), flunixin meglumine (Banamine), dexamethasone, and procaine penicillin G -- by applying a standard per-kilogram dose rate to the horse's body weight. Which medication you select is by far the biggest factor in the result: the modeled rates span more than a 400-fold range, from dexamethasone's roughly 0.05 mg/kg anti-inflammatory dose up to procaine penicillin G's roughly 22 mg/kg antibiotic dose, so switching drugs changes the calculated dose far more than any realistic difference in body weight ever will. Within a single drug, though, the relationship is simple and proportional: a heavier horse gets a larger dose, scaled directly by weight. The Administration Route dropdown only ever offers the routes actually appropriate for the selected medication -- Procaine Penicillin G, for example, offers Intramuscular only, because giving procaine penicillin G intravenously is a well-documented cause of severe, sometimes fatal, CNS reactions in horses. Where a drug does offer more than one route (Bute and Banamine both offer Oral and IV), Route does not change the calculated milligram dose -- it only changes the administration-method label shown alongside the result.
Phenylbutazone's 4.4 mg/kg dose shown here is specifically the standard short loading dose, given for only the first 1-2 days of treatment; the calculator also reports a separate, lower Maintenance Dose (2.2 mg/kg) that veterinarians typically taper to afterward, since sustaining the higher loading dose for a full multi-day course carries real GI ulceration and renal injury risk. Dose volume in mL is the milligram dose divided by the drug's typical commercial concentration (for example, roughly 200 mg/mL for Bute injectable); if that volume would exceed roughly 20 mL -- more than is practical to inject at a single intramuscular site in a horse -- the calculator flags it with a note recommending you ask your veterinarian about splitting the dose across multiple injection sites. This calculator is an estimation aid built from commonly cited standard dose ranges, not a substitute for a veterinary prescription -- actual dosing must account for the individual animal's condition, concurrent medications, kidney and GI health, and the specific product concentration on hand, which can differ from the typical values assumed here. Always confirm dose, route, and duration with a licensed veterinarian before administering any medication to a horse.
Inputs
Results
Dose
2,200 mg
Volume
11 mL
Figures current as of 2026. Sources: FDA-regulated (prescription-only) veterinary drug labeling for flunixin meglumine injectable/oral solution; IM administration is contraindicated due to documented tissue-irritation/myonecrosis risk, Olsén L, Ingvast-Larsson C, Broström H, Larsson P, Tjälve H. "Clinical signs and etiology of adverse reactions to procaine benzylpenicillin and sodium/potassium benzylpenicillin in horses." Journal of Veterinary Pharmacology and Therapeutics, 2007.
How to Use This Calculator
- Enter Horse Weight in kilograms — use a weight tape if scales are unavailable.
- Select the Medication from the dropdown (Bute, Banamine, Dexamethasone, or Procaine Penicillin G).
- Choose Administration Route — the list shows only routes valid for the selected Medication; it does not change the calculated dose amount.
- Review Single Dose (mg) and Volume (mL) — for Phenylbutazone, also review Maintenance Dose (mg) for the tapered amount used after the initial loading period.
- Always confirm the dose with a licensed veterinarian before administration.
How the result changes with Horse Weight
| Horse Weight | Dose | Volume |
|---|---|---|
| 250 | 1,100 mg | 5.5 mL |
| 375 | 1,650 mg | 8.3 mL |
| 750 | 3,300 mg | 16.5 mL |
| 1,200 | 5,280 mg | 26.4 mL |
What each input means
- Horse Weight
- Body weight in kilograms (1 lb = 0.45 kg).
- Medication
- Select the prescribed medication.
- Administration Route
- Route of drug administration as directed by veterinarian. Only routes valid for the selected Medication are offered.
What each result means
- Dose
- Calculated dose per administration (the loading dose for Phenylbutazone).
- Volume
- Injection/oral volume per dose.
- Maintenance Dose
- Phenylbutazone only: the tapered dose given after the 1-2 day loading period. 0 for other medications, which use the same dose for the full course.
- Frequency
- How often to administer.
- Duration
- Standard treatment duration.
- Injection Volume Note
- Flags when the calculated volume exceeds a practical single intramuscular injection-site amount.
How this is calculated
Worked example, using the default values
- Identify Input ParametersHorse Weight = 500, Medication = 1, Administration Route = 1 = 3 input(s) provided
- Calculate DoseDose2200 = 2200
- Calculate VolumeVolume11 = 11
- Calculate FrequencyFrequencyEvery 12 hours = Every 12 hours
- Calculate DurationDuration2 days at the loading dose above, then taper to 2.2 mg/kg (see Maintenance Dose) for the rest of the course = 2 days at the loading dose above, then taper to 2.2 mg/kg (see Maintenance Dose) for the rest of the course
Figures and sources
- Flunixin meglumine (Banamine) equine NSAID dose — 1.1 mg/kg, oral or IV only (not IM), for up to 5 days (2026) — FDA-regulated (prescription-only) veterinary drug labeling for flunixin meglumine injectable/oral solution; IM administration is contraindicated due to documented tissue-irritation/myonecrosis risk
- Procaine penicillin G in horses — intramuscular-only administration; accidental intravascular injection causes CNS ("procaine") reactions (2007) — Olsén L, Ingvast-Larsson C, Broström H, Larsson P, Tjälve H. "Clinical signs and etiology of adverse reactions to procaine benzylpenicillin and sodium/potassium benzylpenicillin in horses." Journal of Veterinary Pharmacology and Therapeutics, 2007.
Engine last updated . Checked against 4 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does changing the Medication dropdown move the dose so much more than Horse Weight does?
The four modeled drugs use dose rates that differ by more than 400-fold -- dexamethasone is dosed around 0.05 mg per kilogram while procaine penicillin G is dosed around 22 mg per kilogram -- so switching the Medication selection swings the calculated milligram dose far more than any realistic change in Horse Weight. Within one selected drug, though, the dose scales directly and proportionally with the horse's weight, so a heavier horse always receives a larger dose for the same medication.
Does changing the Administration Route change the calculated dose, and why can't every route be selected for every drug?
No, Route never changes the calculated milligram dose for these four drugs. The Administration Route dropdown also only offers the routes that are actually appropriate for whichever medication you've selected -- Procaine Penicillin G, for example, offers Intramuscular only, because giving procaine penicillin G intravenously is a well documented cause of severe, sometimes fatal, CNS ("procaine") reactions in horses, catalogued in veterinary pharmacology literature such as Olsén et al.'s 2007 case series in the Journal of Veterinary Pharmacology and Therapeutics. Selecting a different, valid route only changes which administration method is displayed alongside the result, never the milligram total.
Where do the standard dose rates in this calculator come from?
They reflect commonly cited standard dose ranges from equine veterinary pharmacology references for each drug's typical indication -- phenylbutazone's 4.4 mg/kg dose is the standard short loading dose used for the first 1-2 days before tapering to a 2.2 mg/kg maintenance dose, and flunixin meglumine's 1.1 mg/kg dose is the FDA-approved once-daily rate for musculoskeletal pain. Actual prescribed doses can differ based on the individual horse's condition, concurrent medications, and the judgment of the treating veterinarian, so treat this as a starting estimate, not a final prescription.
Why does the calculator show a Volume in mL as well as a Dose in mg?
Injectable and oral liquid medications are measured out by volume, not by weight, so the calculator divides the milligram dose by the drug's typical commercial concentration (for example, roughly 200 mg per mL for Bute) to show how many milliliters that translates to. If the resulting volume would exceed roughly 20 mL for an intramuscular injection -- more than is practical to give at a single site in a horse -- the calculator adds a note recommending you ask your veterinarian about splitting the dose across multiple sites. Always confirm the actual concentration printed on the product label you're using, since concentrations can vary between manufacturers and formulations.
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