Quantitation of fluphenazine in equine serum following fluphenazine decanoate administration

Fluphenazine, a potent antipsychotic used to treat schizophrenia in humans, is used in racehorses as a performance-enhancing drug, and for that reason it has been banned by the Association of Racing Commissioners International. A liquid chromatography-tandem mass spectrometry method for detecting and quantitating fluphenazine in equine serum was developed and validated. The method was then employed to quantitate fluphenazine in serum samples collected from three study horses after intramuscular injection of fluphenazine decanoate. Stability testing showed that fluphenazine is stable in unextracted and processed samples as well as samples that have been subjected to up to three freeze-thaw cycles. The limit of detection and lower limit of quantitation of fluphenazine were determined to be 0.05 and 0.1 ng/mL, respectively. Precision was evaluated based on one-way analysis of variance of replicate quality control samples and was determined to be 27.2% at the 0.2 ng/mL level and 18.1% at the 2 ng/mL level. Bias was determined to be 0.55% at the 0.2 ng/mL level and 3.66% at the 2 ng/mL level. In two of three horses, fluphenazine was detected in serum up to 14 days post-administration. The highest detected concentration of fluphenazine in serum was 1.4 ng/mL.