Enantiomeric composition analysis of pranoprofen in equine plasma and urine by chiral liquid chromatography–tandem mass spectrometry in selected reaction monitoring mode

The enantioseparation of pranoprofen after its addition in racemic form into equine plasma and urine was conducted by chiral liquid chromatography–tandem mass spectrometry in selected reaction monitoring mode. The methods for the assay of both enantiomers were linear (r ≥ 0.9943) in the low range from 0.001 to 0.1 μg/mL and high range from 0.01 to 1.0 μg/mL with good precision (% RSD ≤ 5.6) and accuracy (% RE = −5.3 to 1.9). When racemic pranoprofen was orally administered to four horses at a single dose of 3.1 mg/kg, the median plasma concentrations of (R)-pranoprofen were lower than the levels of (S)-pranoprofen from start to finish. In contrast, the urinary level of (R)-pranoprofen was 2.5 fold higher than (S)-pranoprofen level for the first 6 h, followed by its rapid decrease down below (S)-pranoprofen concentration. Monitoring of the R/S ratios in equine urine may be useful for the prevention of false positive in horse doping test.