The Analysis of Phenylbutazone and Its Active Metabolite, Oxyphenbutazone, in Equine Tissues (Muscle, Kidney, and Liver), Urine, and Serum by LC-MS/MS.

The research article presents the methodology and results of a study examining the residue depletion profile of the drug phenylbutazone and its metabolite oxyphenbutazone in equine tissues and fluids, using two types of LC-MS/MS methods.

Methodology

• The researchers utilized two validated Liquid chromatography–mass spectrometry (LC-MS/MS) methods to monitor the residue depletion of the drugs phenylbutazone (PBZ) and its metabolite oxyphenbutazone (OXPBZ) from equine (horse) tissues and fluids.
• One LC-MS/MS method, with a limit of quantitation (LOQ) of 1.0ng/mL for PBZ and 2.0ng/mL for OXPBZ, was used to analyze the presence of the two drugs in equine urine and blood serum.
• The other LC-MS/MS method, with an LOQ of 0.5 ng/g for PBZ and OXPBZ, was used to analyze the presence of the drugs in equine tissue samples, namely muscle, kidney, and liver tissues.

Experimentation

• Two horses were given an intravenous dose of 8.8 mg/kg PBZ for four days consecutively. They were then humanely sacrificed at a slaughter plant seven days after the final drug administration.
• Urine, blood serum, and tissue samples from the kidney, liver, and muscle of these two horses, were collected, shipped on ice to the lab, and stored at -20°C until they were needed for analysis.

Data Collection

• The researchers then employed the two aforementioned LC-MS/MS methods, coupled with deuterated internal standards, to measure concentrations of PBZ and OXPBZ residues in the collected specimens.

Results and Conclusions

• The results of this research indicated that the established LC-MS/MS methods were adequate in studying the depletion kinetics, i.e., the rate at which a drug is removed from the body, of PBZ residues in horse tissues and fluids.