title: Enantioselective analysis of unbound tramadol, O-desmethyltramadol and N-desmethyltramadol in plasma by ultrafiltration and LC-MS/MS: application to clinical pharmacokinetics.
abstract: This study describes the enantioselective analysis of unbound and total concentrations of tramadol and its main metabolites O-desmethyltramadol (M1) and N-desmethyltramadol (M2) in human plasma. Sample preparation was preceded by an ultrafiltration step to separate the unbound drug. Both the ultrafiltrate and plasma samples were submitted to liquid/liquid extraction with methyl t-butyl ether. Separation was performed on a Chiralpak(®) AD column and tandem mass spectrometry consisting of an electrospray ionization source, positive ion mode and multiple reaction monitoring was used as the detection system. Linearity was observed in the following ranges: 0.2-600 and 0.5-250 ng/mL for analysis of total and unbound concentrations of the tramadol enantiomers, respectively, and 0.1-300 and 0.25-125 ng/mL for total and unbound concentrations of the M1 and M2 enantiomers, respectively. The lower limits of quantitation were 0.2 and 0.5 ng/mL for analysis of total and unbound concentration of each tramadol enantiomer, respectively, and 0.1 and 0.25 ng/mL for total and unbound concentrations of M1 and M2 enantiomers, respectively. Intra- and interassay reproducibility and inaccuracy did not exceed 15%. Clinical application of the method to patients with neuropathic pain showed plasma accumulation of (+)-tramadol and (+)-M2 after a single oral dose of racemic tramadol. Fractions unbound of tramadol, M1 or M2 were not enantioselective in the patients investigated.
authors.affiliation: Departamento de Análises Clínicas, Toxicológicas e Bromatológicas, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil.
authors.forename: Natália Valadares
authors.initials: NV
authors.lastname: de Moraes
authors.forename: Gabriela Rocha
authors.initials: GR
authors.lastname: Lauretti
authors.forename: Marcio Nogueira
authors.initials: MN
authors.lastname: Napolitano
authors.forename: Naiane Ribeiro
authors.initials: NR
authors.lastname: Santos
authors.forename: Ana Leonor Pardo Campos
authors.initials: AL
authors.lastname: Godoy
authors.forename: Vera Lucia
authors.initials: VL
authors.lastname: Lanchote
mesh_terms: D000328:Adult; D000701:Analgesics, Opioid / Q000097:blood / Q000493:pharmacokinetics; D002853:Chromatography, Liquid / Q000379:methods*; D005260:Female; D006801:Humans; D057230:Limit of Detection; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D009437:Neuralgia / Q000097:blood / Q000188:drug therapy; D015203:Reproducibility of Results; D013237:Stereoisomerism; D053719:Tandem Mass Spectrometry / Q000379:methods*; D014147:Tramadol / Q000031:analogs & derivatives* / Q000097:blood / Q000493:pharmacokinetics*; D014462:Ultrafiltration / Q000379:methods*
chemical_list: D000701:Analgesics, Opioid; C080580:O-demethyltramadol; D014147:Tramadol; C080579:N-demethyltramadol