Phenylbutazone: veterinary dose and monograph

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

• 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

• 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

• 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

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

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

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

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
• Meloxicam
• Methylprednisolone Acetate
• Nimesulide
• Piroxicam
• Prednisolone
• Robenacoxib
• Tolfenamic Acid

Frequently asked questions