PHENYLBUTAZONE IN RACING GREYHOUNDS - PLASMA AND URINARY RESIDUES 24 AND 48 HOURS AFTER A SINGLE INTRAVENOUS ADMINISTRATION

The concentrations of phenylbutazone (PBZ), oxyphenbutazone (OPBZ) and gammahydroxyphenylbutazone (OHPBZ) in plasma and urine from 50 Greyho unds 24 and 48 h after the intravenous administration of a single dose of PBZ (30 mg/kg) were measured. The 24 h plasma concentrations of OP BZ and OHPBZ, the 48 h plasma concentration of OHPBZ and the 24 h urin ary concentration of PBZ were normally distributed, while log transfor mations were required before the 24 h plasma concentration of PBZ and the 24 and 48 h urinary concentrations of OPBZ and OHPBZ became normal ly distributed, The 95%, 99%, 99.9% and 99.99% upper predicted confide nce intervals for both 24 h and 48 h plasma and urinary concentrations demonstrated wide potential variation in the concentration of the ana lytes should PBZ be administered to Greyhounds. The 24 h plasma and ur inary concentrations of PBZ were weakly correlated, but no similar rel ationship existed for OPBZ or OHPBZ. The urinary concentrations of eac h analyte were not affected by the trainer or sex of the Greyhound or the urinary pH, We conclude that it would be impossible to predict the timing of the PBZ administration or the plasma concentration of PBZ f rom the measurement of the concentration of PBZ in a single sample of urine.