title: Determination of duloxetine in human plasma with proven lack of influence of the major metabolite 4-hydroxyduloxetine.
abstract: OBJECTIVE
  Minimizing the impact of major or unstable metabolites on the determination of a drug substance represents a leading task in the development and validation of bioanalytical methods. "Incurred samples reanalysis" provides relevant information too late; therefore, carefully selected tests on known metabolites should precede the pharmacokinetic studies.
  
  
  METHODS
  This paper describes a simple and rapid HPLC-UV method for the determination of duloxetine, a potent serotonin and norepinephrine reuptake inhibitor, in the presence of its major metabolite, i.e. 4-hydroxyduloxetine glucuronide. Analyte and fluoxetine (internal standard) were extracted from human plasma by liquid-liquid extraction.
  
  
  RESULTS
  No influence of the major metabolite was observed on the reliability of the new method. There was also lack of evidence of the major metabolite back-conversion to the parent drug substance. The validation demonstrated high precision of the new method. All validation parameters met the acceptance criteria of bioanalytical regulations.
  
  
  CONCLUSIONS
  The new method enabled the reliable determination of duloxetine in the presence of its major metabolite in the human plasma. The method might be applied to pharmacokinetic studies in humans, including bioequivalence and therapeutic drug monitoring.
authors.affiliation: Pharmaceutical Research Institute, Pharmacology Department, 8 Rydygiera, 01-793 Warsaw, Poland. Electronic address: m.kaza@ifarm.eu.
authors.forename: Michał
authors.initials: M
authors.lastname: Kaza
authors.affiliation: Pharmaceutical Research Institute, Pharmacology Department, 8 Rydygiera, 01-793 Warsaw, Poland.
authors.forename: Edyta
authors.initials: E
authors.lastname: Gilant
authors.affiliation: Pharmaceutical Research Institute, Pharmacology Department, 8 Rydygiera, 01-793 Warsaw, Poland; Medical University of Warsaw, Department of Drug Chemistry, 1 Banacha, 02-097 Warsaw, Poland.
authors.forename: Monika
authors.initials: M
authors.lastname: Filist
authors.affiliation: Medical University of Warsaw, Department of Drug Chemistry, 1 Banacha, 02-097 Warsaw, Poland.
authors.forename: Iwona
authors.initials: I
authors.lastname: Szlaska
authors.affiliation: Medical University of Warsaw, Department of Drug Chemistry, 1 Banacha, 02-097 Warsaw, Poland.
authors.forename: Tomasz
authors.initials: T
authors.lastname: Pawiński
authors.affiliation: Pharmaceutical Research Institute, Pharmacology Department, 8 Rydygiera, 01-793 Warsaw, Poland.
authors.forename: Piotr J
authors.initials: PJ
authors.lastname: Rudzki
mesh_terms: D002851:Chromatography, High Pressure Liquid / Q000379:methods; D016903:Drug Monitoring / Q000379:methods; D000068736:Duloxetine Hydrochloride; D006801:Humans; D059625:Liquid-Liquid Extraction / Q000379:methods; D010949:Plasma / Q000737:chemistry*; D015203:Reproducibility of Results; D013876:Thiophenes / Q000737:chemistry*; D014466:Ultraviolet Rays
chemical_list: D013876:Thiophenes; D000068736:Duloxetine Hydrochloride
keywords: 4-Hydroxyduloxetine glucuronide; HPLC; Metabolite back-conversion; Pharmacokinetics; Validation