phenylbutazone

Phenylbutazone is a nonsteroidal anti-inflammatory drug (NSAID) that has been used to treat pain and inflammation. It gained widespread use in humans in the mid-20th century for conditions such as rheumatoid arthritis and other musculoskeletal disorders, but its safety profile led to significant restrictions. Today, phenylbutazone is largely no longer approved for human use in many countries due to serious adverse effects, and it remains available mainly for veterinary use, particularly in horses.

Pharmacology and mechanism of action: Like other NSAIDs, phenylbutazone inhibits cyclooxygenase enzymes, resulting in decreased synthesis of prostaglandins. This reduces inflammation, pain, and fever. It is considered non-selective with respect to COX enzymes, contributing to both therapeutic effects and potential adverse effects on the gastrointestinal tract, kidneys, and other organs.

Clinical use: In humans, phenylbutazone was once a common analgesic and anti-inflammatory agent but is now rarely used because of safety concerns. In veterinary medicine, it is employed to alleviate pain and inflammation associated with musculoskeletal disorders in horses and some other animals. Dosing and withdrawal times are species-specific and tightly regulated to ensure food safety in meat- and milk-producing animals.

Adverse effects and safety concerns: The drug carries a risk of serious gastrointestinal injury, including ulcers and bleeding. It can cause liver and kidney toxicity, hematologic problems such as agranulocytosis or aplastic anemia, and hypersensitivity or severe skin reactions in rare cases. The risk of adverse events is higher in older individuals, those with preexisting kidney or liver disease, and when combined with other NSAIDs or certain medications. Because of these risks, many regulatory agencies restrict or prohibit its use in humans.

Regulatory status: Phenylbutazone is generally not approved for human use in the United States and many other countries, but it remains permitted for veterinary use under regulated conditions.