Phenylbutazone

Phenylbutazone In Dogs & Cats: Uses, Dosage and Side Effects

Overview

• Non-selective COX enzyme inhibitor, limiting prostaglandin production.

Uses of Phenylbutazone

• Management of mild to moderate pain and inflammation in osteoarthritic conditions.

Dose of Phenylbutazone in Dogs and Cats

Dogs:

• 2–20 mg/kg p.o. q8–12h.
• Maximum dose 800 mg.
• The manufacturers recommend a starting dose of 10 mg/kg twice daily for 7 days, reducing to 5 mg/kg twice daily thereafter.
• The 200 mg tablet strength should not be used in dogs weighing <20 kg.
• The 100 mg tablet strength should not be used in dogs weighing <5 kg.

Cats:

• Do not use.

Side Effects of Phenylbutazone in Dogs and Cats

• GI signs may occur in all animals after NSAID administration.
• Stop therapy if this persists beyond 1–2 days.
• Some animals develop signs with one NSAID and not another.
• A 3–5 day wash-out period should be allowed before starting another NSAID
  after cessation of therapy.
• Stop therapy immediately if GI bleeding is suspected.
• There is a small risk that NSAIDs precipitate cardiac failure in humans and this risk in animals is unknown.
• Phenylbutazone may infrequently cause bone marrow suppression, including aplastic
  anaemias.
• It may also cause false low T3 and T4 values.

Contraindications of Phenylbutazone in Dogs and Cats

• Do not give to dehydrated, hypovolaemic or hypotensive patients or those with GI disease or blood clotting problems.
• Do not administer perioperatively until the animal is fully recovered from anaesthesia and normotensive.
• Do not give to pregnant animals or animals <6 weeks of age.

Some Notes:

• Do not administer concurrently or within 24 hours of other NSAIDs and glucocorticoids.
• Do not administer with other potentially nephrotoxic agents, e.g. aminoglycosides.
• Not selective for COX-2 and is likely to cause more adverse effects than more selective COX-2 inhibitors that have superseded the use of phenylbutazone.
• Not authorized for preoperative administration to dogs.
• Liver disease will prolong the metabolism of phenylbutazone, leading to the potential for drug accumulation and overdose with repeated dosing.
• Administration of phenylbutazone to animals with renal disease must be carefully evaluated.
• Do not use in cats.