Phenylbutazone is a nonsteroidal anti-inflammatory drug (NSAID) and cyclooxygenase inhibitor. It is a potent pain reliever, antipyretic, and anti-inflammatory. In the horse, it is used commonly for lameness, resulting from soft-tissue injury, muscle soreness, bone and joint problems, and laminitis. NSAIDs work by inhibiting the body’s production of prostaglandins, thromboxane, and other inflammatory mediators. Some of these actions may be dose-dependent. Phenylbutazone may be given intravenously or orally; pain relief and fever reduction usually starts within one to two hours.