Analysis of tolfenpyrad and its metabolites in plasma in a tolfenpyrad poisoning case

Tolfenpyrad (TFP) is a pesticide that was first approved in 2002 in Japan under the trade name of Hachi-hachi. Analyses of TFP and its major metabolite, 4-[4-[(4-chloro-3-ethyl-1-methylpyrazol-5-yl)carbonylaminomethyl]phenoxy]benzoic acid (PTCA), in plasma obtained from a cadaver suspected to have died of TFP poisoning, were conducted by liquid chromatography-mass spectrometry. The existence of TFP and PTCA was confirmed by scan mode and quantitative analysis was performed by selected ion monitoring mode. Calibration curves showed good linearity over the range of 0.1-4 and 0.25-4 µg/mL, and concentrations were estimated to be 1.97 ± 0.02 and 2.88 ± 0.04 µg/mL for TFP and PTCA, respectively. The plasma extract was further examined to find other metabolites using quadrupole time-of-flight MS, and the results revealed three more metabolites, which were suggested to be hydroxy-TFP, dehydro-TFP and hydroxy-PTCA. Plausible metabolic pathways of TFP in humans are: (i) oxidation of the methyl group on the benzene ring, and (ii) hydroxylation followed by dehydration at the ethyl group on the pyrazole ring.