# Phenylbutazone: veterinary dose and monograph

> Phenylbutazone is a veterinary anti-inflammatory drug. Pyrazolone NSAID — non-selective COX inhibitor, the workhorse equine musculoskeletal NSAID. Indications include equine musculoskeletal inflammation — lameness, OA, tendinitis, laminitis (chronic phase); equine fever associated with infection (limited use); equine colic — analgesia (less popular than flunixin). This monograph lists 5 reference doses for dogs, cats and horses, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/phenylbutazone · Last reviewed: 2026-10-01

## At a glance

- **Drug class:** Anti-inflammatory
- **Also known as:** Bute, Butazolidin, Phenylzone
- **Species with doses:** Dogs, Cats and Horses
- **General dose range:** 2.2–8.8 mg/kg PO q12h × 4–7 d — check the species tables for the indication
- **Routes:** PO, IV
- **Last reviewed:** 1 October 2026

## Indications

- Equine musculoskeletal inflammation — lameness, OA, tendinitis, laminitis (chronic phase)
- Equine fever associated with infection (limited use)
- Equine colic — analgesia (less popular than flunixin)
- Canine OA (historical use — newer NSAIDs preferred)

## Phenylbutazone dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

### Dogs

*Phenylbutazone doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Pain / inflammation (Plumb's, historical) | 14 mg/kg | PO | q8h initial then taper | — |

- Pain / inflammation (Plumb's, historical): Plumb’s p.964 (label): 14 mg/kg PO three times daily initially, maximum 800 mg/day regardless of weight, then titrate to the lowest effective dose; 15–22 mg/kg PO q12h (Posner & Papich). Papich 5e: 15–22 mg/kg q8–12h PO or IV (44 mg/kg/day; 800 mg/dog maximum). Plumb’s: little reason to use it now that safer approved NSAIDs exist — bone-marrow suppression risk.

### Cats

*Phenylbutazone doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Anti-inflammatory (rarely used) | 6–8 mg/kg | PO | q12h | — |

- Anti-inflammatory (rarely used): Papich 5e: cats 6–8 mg/kg q12h IV or PO. Safer approved NSAIDs are preferred; monitor for GI and haematological toxicity.

### Horses

*Phenylbutazone doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Acute lameness / inflammation | 4.4 mg/kg | PO | q12h | 2–3 days, then taper |
| Maintenance / chronic OA | 2.2 mg/kg | PO | q12h, then q24h | — |
| IV therapy | 2.2–4.4 mg/kg | IV | q24h | 48–96 h (max 5 days) |

- Acute lameness / inflammation: Papich 5e: 4.4–8.8 mg/kg PER DAY (generally 2–4 g per horse) — typically 4.4 mg/kg q12h for the first 2–3 days, tapering to 2.2 mg/kg q12h (1 g per horse) and then once daily; do not use the top dose for more than 48–96 h. Plumb’s p.964 (label): 2–4 g PO per 454 kg per day, never more than 4 g/day. (The previous 8.8 mg/kg q12h doubled the maximum daily dose.)
- Maintenance / chronic OA: Papich 5e: taper to 2.2 mg/kg q12h (≈1 g per horse) and eventually once daily. Plumb’s p.964: osteoarthritis — minimal dose 2.2 mg/kg PO twice daily (Laverty 2008). Use the lowest effective dose; GI ulceration, right dorsal colitis and renal papillary necrosis with chronic use.
- IV therapy: Papich 5e: injection 2.2–4.4 mg/kg/day for 48–96 h, IV only — IM injection causes tissue irritation. Plumb’s p.964 (label): 1–2 g IV per 454 kg, given slowly, for no more than 5 successive days; then oral. Perivascular injection causes severe sloughing.

## Contraindications

PROHIBITED in any animal intended for human consumption (food animals — long tissue residence; carcinogenic concerns in humans). Pre-existing GI ulcers, hepatic / renal disease, bone marrow disorders. Hypersensitivity. Dehydration. Dogs: newer COX-2 selective NSAIDs preferred — bute is not recommended in dogs by current standard of care.

## Species-specific warnings

> **Caution:** Horses: Workhorse equine NSAID. Right dorsal colitis is the catastrophic complication — limit duration, monitor TP and faecal blood.

> **Caution:** Cattle: PROHIBITED in food-producing animals — long tissue residence and human carcinogenicity concerns.

> **Caution:** Dogs: Largely obsolete — newer COX-2-selective NSAIDs (carprofen, meloxicam, firocoxib) are safer and preferred.

## Adverse effects

- GI ulceration — right dorsal colitis in horses (most serious complication; sudden onset diarrhoea / colic / hypoproteinaemia)
- Renal papillary necrosis (especially with dehydration)
- Hepatic toxicity
- Bone marrow suppression (long-term, dogs)
- Oral / oesophageal irritation from undissolved paste / powder
- Hypoproteinaemia / oedema (chronic use)

## Drug interactions

- Other NSAIDs (flunixin, ketoprofen): additive GI / renal toxicity — DO NOT combine
- Corticosteroids: additive GI ulceration — DO NOT combine
- Warfarin / oral anticoagulants: phenylbutazone displaces warfarin from albumin → bleeding risk
- Aminoglycosides: additive nephrotoxicity in dehydrated patients
- Furosemide: synergistic renal injury
- Methotrexate: phenylbutazone reduces methotrexate clearance

## Pregnancy and lactation

AVOID in pregnancy — fetal prostaglandin synthesis essential for normal cardiac and renal development. Use alternative NSAIDs (flunixin per Plumb's safer profile) or refer if absolutely necessary.

## Monitoring

- Serum creatinine / urea — baseline and every 7 days during therapy
- CBC every 14 days for prolonged courses
- Faecal occult blood / clinical GI signs
- Total protein / albumin — drops in right dorsal colitis
- Hepatic enzymes (GGT, AST in horses; ALT in dogs)

## Toxicity and overdose

Right dorsal colitis in horses (3–10 days into therapy): sudden colic, diarrhoea, hypoproteinaemia, ventral oedema. Mortality 50 %. Dogs: GI ulceration, hepatic toxicity, bone marrow suppression. Carcinogenic in humans (agranulocytosis, aplastic anaemia) — WEAR GLOVES when handling paste / powder.

Management: Stop drug. Sucralfate 1 g PO q6h (horse) or 0.5–1 g PO q8h (dog) for GI protection. Omeprazole 4 mg/kg PO q24h. IV crystalloid for renal protection. Plasma transfusion if severe hypoproteinaemia (right dorsal colitis). CBC monitoring for bone marrow recovery.

## Clinical pearls

- Acute equine lameness: 4.4 mg/kg PO BID day 1 → 2.2 mg/kg PO BID days 2–4 — most horses respond, taper after acute phase
- NEVER combine bute with flunixin or another NSAID — right dorsal colitis risk multiplies
- Always pair chronic bute with omeprazole 4 mg/kg PO q24h for GI protection
- PROHIBITED in food animals in most jurisdictions — never give to a cow, sheep, or goat that may enter the food chain
- Dogs: phenylbutazone is largely obsolete — use carprofen / meloxicam / firocoxib instead
- Wear gloves with paste / powder — human aplastic anaemia is the reason this drug was pulled from human medicine

## Mechanism of action

Non-selective COX-1 / COX-2 inhibitor — reduces prostaglandin synthesis → anti-inflammatory, analgesic, antipyretic. The COX-1 inhibition is the source of GI ulceration and renal papillary necrosis with chronic use. High plasma protein binding (~98 %) → displaces other protein-bound drugs.

## Formulations and products

- Bute paste 12 g per 32 g tube (≈ 1 g/syringe-mark)
- Bute tablet 1 g
- Phenylbutazone injection 200 mg/mL (equine)
- Phenylbutazone oral powder 1 g per 10 g of powder (100 mg/g), mixed into feed (Phenylbute — Plumb’s p.965)

## Storage

15–25 °C protected from light. Paste / powder: tightly closed. Multidose injection: discard 28 d after broaching.

## Before you use this dose

> **Caution:** Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

## Other anti-inflammatory drugs

- [Mavacoxib](https://vetmasterji.com/drugs/mavacoxib)
- [Meloxicam](https://vetmasterji.com/drugs/meloxicam)
- [Methylprednisolone Acetate](https://vetmasterji.com/drugs/methylprednisolone)
- [Nimesulide](https://vetmasterji.com/drugs/nimesulide)
- [Piroxicam](https://vetmasterji.com/drugs/piroxicam)
- [Prednisolone](https://vetmasterji.com/drugs/prednisolone)
- [Robenacoxib](https://vetmasterji.com/drugs/robenacoxib)
- [Tolfenamic Acid](https://vetmasterji.com/drugs/tolfenamic-acid)

## Frequently asked questions

### What is the dose of Phenylbutazone for dogs?

Reference doses for Phenylbutazone in dogs: 14 mg/kg PO q8h initial then taper (Pain / inflammation (Plumb's, historical)). Confirm against the label and the patient before use.

### What is the dose of Phenylbutazone for cats?

Reference doses for Phenylbutazone in cats: 6–8 mg/kg PO q12h (Anti-inflammatory (rarely used)). Confirm against the label and the patient before use.

### What is the dose of Phenylbutazone for horses?

Reference doses for Phenylbutazone in horses: 4.4 mg/kg PO q12h for 2–3 days, then taper (Acute lameness / inflammation); 2.2 mg/kg PO q12h, then q24h (Maintenance / chronic OA); 2.2–4.4 mg/kg IV q24h for 48–96 h (max 5 days) (IV therapy). Confirm against the label and the patient before use.

### When should Phenylbutazone not be used?

PROHIBITED in any animal intended for human consumption (food animals — long tissue residence; carcinogenic concerns in humans). Pre-existing GI ulcers, hepatic / renal disease, bone marrow disorders. Hypersensitivity. Dehydration. Dogs: newer COX-2 selective NSAIDs preferred — bute is not recommended in dogs by current standard of care.

### What are the side effects of Phenylbutazone in animals?

GI ulceration — right dorsal colitis in horses (most serious complication; sudden onset diarrhoea / colic / hypoproteinaemia); Renal papillary necrosis (especially with dehydration); Hepatic toxicity; Bone marrow suppression (long-term, dogs); Oral / oesophageal irritation from undissolved paste / powder; Hypoproteinaemia / oedema (chronic use).

## Sources

- Plumb's Veterinary Drug Handbook
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.