Phenylbutazone (Bute) is a pyrazolone derivative that was one of the first non-steroidal anti-inflammatory drugs (NSAIDs) approved for use in horses and dogs. The use of bute in food producing animals is prohibited in most countries, including the European Union, United States, Canada and Japan. As a result, MRLs have not been set for phenylbutazone residues, meaning that any detection is considered a violation.
| Assay | LOD (ppb) | Compound | Cross Reactivity % |
|---|---|---|---|
| Phenylbutazone | 2.01 (Serum) 1.00 (Tissue) | Phenylbutazone* Oxyphenbutazone | 100.00 156.00 |