title: Methadone concentrations in blood, plasma, and oral fluid determined by isotope-dilution gas chromatography-mass spectrometry.
abstract: Methadone (MTD) is widely used for detoxification of heroin addicts and also in pain management programs. Information about the distribution of methadone between blood, plasma, and alternative specimens, such as oral fluid (OF), is needed in clinical, forensic, and traffic medicine when analytical results are interpreted. We determined MTD and its metabolite 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) in blood, plasma, blood cells, and OF by gas chromatography-mass spectrometry (GC-MS) after adding deuterium-labeled internal standards. The analytical limits of quantitation for MTD and EDDP by this method were 20 and 3 ng/mL, respectively. The amounts of MTD and EDDP were higher in plasma (80.4 % and 76.5 %) compared with blood cells (19.6 % and 23.5 %) and we found that repeated washing of blood cells with phosphate-buffered saline increased the amounts in plasma (93.6 % and 88.6 %). Mean plasma/blood concentration ratios of MTD and EDDP in spiked samples (N = 5) were 1.27 and 1.21, respectively. In clinical samples from patients (N = 46), the concentrations of MTD in plasma and whole blood were highly correlated (r = 0.92, p < 0.001) and mean (median) plasma/blood distribution ratios were 1.43 (1.41). The correlations between MTD in OF and plasma (r = 0.46) and OF and blood (r = 0.52) were also statistically significant (p < 0.001) and the mean OF/plasma and OF/blood distribution ratios were 0.55 and 0.77, respectively. The MTD concentration in OF decreased as salivary pH increased (more basic). These results will prove useful in clinical and forensic medicine when MTD concentrations in alternative specimens are compared and contrasted.
authors.affiliation: Department of Medical Laboratory Science and Biotechnology, Fooyin University, Ta-Liao, Kaohsiung, Taiwan.
authors.forename: Ya-Ching
authors.initials: YC
authors.lastname: Hsu
authors.forename: Bud-Gen
authors.initials: BG
authors.lastname: Chen
authors.forename: Shu-Ching
authors.initials: SC
authors.lastname: Yang
authors.forename: Yu-Shan
authors.initials: YS
authors.lastname: Wang
authors.forename: Shiao-Ping
authors.initials: SP
authors.lastname: Huang
authors.forename: Mei-Han
authors.initials: MH
authors.lastname: Huang
authors.forename: Tai-Jui
authors.initials: TJ
authors.lastname: Chen
authors.forename: Hsu-Chun
authors.initials: HC
authors.lastname: Liu
authors.forename: Dong-Liang
authors.initials: DL
authors.lastname: Lin
authors.forename: Ray H
authors.initials: RH
authors.lastname: Liu
authors.forename: A Wayne
authors.initials: AW
authors.lastname: Jones
mesh_terms: D000701:Analgesics, Opioid / Q000032:analysis* / Q000097:blood*; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D006801:Humans; D057230:Limit of Detection; D008691:Methadone / Q000032:analysis* / Q000097:blood*; D011759:Pyrrolidines / Q000032:analysis* / Q000097:blood*; D012463:Saliva / Q000737:chemistry
chemical_list: D000701:Analgesics, Opioid; D011759:Pyrrolidines; D008691:Methadone; C010724:2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine