Phenylbutazone
Phenylbutazone is a nonsteroidal anti-inflammatory drug.
Group
Nonsteroidal anti-inflammatory drug
Mechanism of Action
Inhibits cyclooxygenase-dependent prostaglandin production, reducing pain and inflammation.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Musculoskeletal pain | Reference only | PO | 15-22 mg/kg every 8-12 hours orally with total no greater than 44 mg/kg/day and 800 mg/day. Both daily ceilings require a linked daily-exposure protocol. | |
| Musculoskeletal pain | Reference only | IV | 15-22 mg/kg every 8-12 hours IV with total no greater than 44 mg/kg/day and 800 mg/day. Both daily ceilings require a linked daily-exposure protocol. | |
| Musculoskeletal pain — Initial | 14 mg/kg | PO | Every 8 h | Maximum 800 mg/day; Taper to minimum effective exposure; newer safer alternatives are generally preferred. The daily ceiling applies to the combined amount of all doses. |
| Musculoskeletal pain | 15–22 mg/kg | PO | Every 12 h | Maximum 800 mg/day; The daily ceiling applies to the combined amount of all doses. |
| Analgesia | 1–5 mg/kg | PO | Every 8 h |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Pain and inflammation | 6–8 mg/kg | IV, PO | Every 12 h |
Horses
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Musculoskeletal pain — Initial | 4.4 mg/kg | PO, IV | Every 12 h | Up to 3 days; Initial 2-3 days only; then reduce. Highest daily doses should not continue beyond 48-96 hours. |
| Musculoskeletal pain — Maintenance | 2.2–3.3 mg/kg | PO | Every 12 h | Tapered alternative after initial response. |
| Musculoskeletal pain — Maintenance | 2.2 mg/kg | PO | Every 24 h | Longer-term lower-dose alternative. |
| Parenteral pain treatment | 2.2–4.4 mg/kg | IV | Every 24 h | Up to 4 days; Reported daily IV regimen for 48-96 hours only; never IM. |
| Pleuropneumonia-associated pain or fever | 2.2–4.4 mg/kg | PO, IV | Every 12 h | |
| Osteoarthritis | 2.2 mg/kg | PO | Every 12 h |
Cattle
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Pain and inflammation — Loading | 17–25 mg/kg | PO, IV | Once | |
| Pain and inflammation — Maintenance | 2.5–5 mg/kg | PO, IV | Every 24 h | |
| Pain and inflammation — Maintenance | 10–14 mg/kg | PO, IV | Every 48 h | |
| Pain and inflammation — Loading | 10–20 mg/kg | PO | Once | |
| Pain and inflammation — Maintenance | 10 mg/kg | PO | Every 48 h |
Pigs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Pain and inflammation | 4 mg/kg | IV, PO | Every 24 h |
Indications
- Musculoskeletal pain and inflammation
- Musculoskeletal pain
- Analgesia
- Pleuropneumonia-associated pain or fever
- Osteoarthritis
- Pain and inflammation
Contraindications
- Gastrointestinal ulceration or renal compromise/dehydration
- Do not inject intramuscularly.
Interactions
- NSAIDs or corticosteroids increase gastrointestinal injury; interferes with equine furosemide response.
Adverse effects
- Gastric ulcers, right dorsal colitis, hypoproteinemia, renal papillary injury and occasional marrow suppression.
Toxicity
Overdose can injure GI mucosa, kidneys, liver and marrow and cause tremor/seizures or acid-base disturbance. Monitor renal function, proteins and fluid tolerance; manage neurologic and GI effects supportively.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Phenylbutazone 100 mg | Tablet | 100 mg / tablet | PO |
| Phenylbutazone 200 mg | Tablet | 200 mg / tablet | PO |
| Phenylbutazone 400 mg | Tablet | 400 mg / tablet | PO |
| Phenylbutazone 1000 mg | Tablet | 1000 mg / tablet | PO |
| Phenylbutazone injection 200 mg/mL | Injection | 200 mg / mL | IV |
Monitoring and Administration
Monitor hydration, CBC, proteins and renal indices. Ponies and draft horses may be more sensitive. Taper after initial control; prolonged high dosing increases harm.
Aqueous compounding is unsuitable because solubility is poor.
Canine older labeling explicitly limits total exposure to 800 mg/day; regimens also constrained by a weight-based daily ceiling must not be widened to allow an unsafe 8-hour high-dose schedule. Equine label alternative is 1-2 g IV per 454 kg, no more than 5 successive IV days, or 2-4 g orally per 454 kg with 4 g/day maximum. Weight-qualified fixed examples and a laminitis 4-g adult-horse loading example are not universal per-animal amounts.