Tris(2‐chloroethyl) Phosphate Pharmacokinetics in the Fischer 344 Rat: A Comparison of Conventional Methods andin VivoMicrodialysis Coupled with Tandem Mass Spectrometry

The pharmacokinetics of tris(2‐chloroethyl) phosphate (TRCP, 20 mg/kg, iv) were investigated in awake male and female and anesthetized male Fischer 344 (F344) rats by conventional (CONV) sampling/detection methods (blood withdrawal with sample workup and analysis for TRCP). TRCP pharmacokinetics were also investigated in anesthetized male F344 rats using a new sampling/detection technique,in vivo microdialysis coupled with tandem mass spectrometry1(MD/MS/MS). The concentration of free TRCP in plasma versus time profiles were analyzed using noncompartmental methods to estimate pharmacokinetic parameters. Comparisons of mean parameter estimates were made for (1) awake males versus females in CONV studies (t test, no significant differences,p< 0.05) and (2) awake and anesthetized males in CONV studies and anesthetized males in MD/MS/MS studies. There were significant differences (Scheffe's test) for the three groups of male rats, most notably the free TRCP concentration in plasma at early time points in CONV versus MD/MS/MS studies. The contributions of an indwelling jugular cannula, the blood sampling regimen, and the in vitro MD/MS/MS standard calibration curve were investigated. It appears that quantitation of TRCP by mass spectrometry using an in vitro standard calibration is responsible for the difference.