The use of phenylbutazone in the horse.

This review presents a brief historical prospective of the genesis of regulated medication in the US racing industry of which the nonsteroidal anti-inflammatory drug (NSAID) phenylbutazone (PBZ) is the focus. It presents some historical guideposts in the development of the current rules on the use of PBZ by racing jurisdictions in the US. Based on its prevalent use, PBZ remains a focus of attention. The review examines the information presented in a number of different models used to determine the effects and duration of PBZ in the horse. They include naturally occurring lameness and reversible-induced lameness models that directly examine the effects and duration of the administration of various doses of PBZ. The review also examines indirect plasma and tissue models studying the suppression of the release of arachidonic acid-derived mediators of inflammation. The majority of studies suggest an effect of PBZ at 24 h at 4.4 mg/kg. This reflects and substantiates the opinion of many clinical veterinarians, many of whom will not perform a prepurchase lameness examination unless the horse is free of NSAID. This remains the opinion of many regulatory veterinarians responsible for the prerace examination of race horses that they wish to examine a horse without the possibility of an NSAID interfering with the examination and masking possible musculoskeletal conditions. Based on scientific studies, residual effects of PBZ remain at 24 h. The impact of sustained effect on the health and welfare of the horse and its contribution to injuries during competition remains problematic.

Screen and confirmation of PEG-epoetin ß in equine plasma.

Methods have been developed to screen for and confirm darbepoetin alfa, recombinant human EPO, and methoxy polyethylene glycol-epoetin ß (PEG-epoetin ß) in horse plasma. All three methods screen samples with an enzyme-linked immunosorbent assay (ELISA) and confirm by liquid chromatography-tandem mass spectrometry (LC-MS/MS). This report focuses on PEG-epoetin ß. The ELISA assay was able to detect PEG-epoetin ß at 0.02 ng/mL in 50 µL of horse plasma. Many samples had high background levels of immunoreactivity; however, introducing polyethylene glycol 6000 (PEG 6000) into the samples before the ELISA assay removed the high background and increased the apparent concentrations of PEG-epoetin ß. In samples collected following the administration of 100 µg of PEG-epoetin ß by the intravenous (IV), intramuscular (IM) and subcutaneous (SC) routes, PEG-epoetin ß was detectable up to 72, 144, and 120 h, respectively. The samples were prepared for LC-MS/MS analysis by extraction with anti-rHuEPO-antibodies-coated Dynabeads followed by digestion with trypsin. The LC-MS/MS confirmation method used the multiple reaction monitoring (MRM) scan mode to monitor four precursor-product ion transitions of the EPO-derived peptide T6. All four transitions of T6 were detectable with S/N > 3. The limit of confirmation for PEG-epoetin ß was 1.0 ng/mL in 2 mL of horse plasma. The method successfully confirmed the presence of PEG-epoetin ß in a sample collected from a Mircera®-treated horse. Compared to PEG-epoetin ß, better sensitivity was achieved for darbepoetin alfa and recombinant human EPO. Darbepoetin alfa was detected in horse plasma four days after IM administration of 100 µg.