title: Development of a HPLC method for the determination of losartan urinary metabolic ratio to be used for the determination of CYP2C9 hydroxylation phenotypes.
abstract: BACKGROUND
  Losartan is metabolized to losartan carboxylic acid (E-3174) by the polymorphic cytochrome CYP2C9. The aim of the study was to develop a high-performance liquid chromatographic (HPLC) method with fluorescence detection for simultaneously measuring losartan and its metabolite E-3174 in urine to evaluate the losartan urinary metabolic ratio (MR: losartan/E-3174) for CYP2C9 phenotyping in humans.
  
  
  METHODS
  The compounds were separated in a reversed-phase chromatographic column and detected by fluorescence at a wavelength of 250 nm for excitation and of 370 nm for emission.
  
  
  RESULTS
  No analytical interferences with endogenous compounds were found, and the extraction recoveries were over 88%. Limits of quantification of 2 ng mL-1 for losartan and 5 ng mL-1 for E-3174 were achieved, as well as good reproducibility with coefficients of variation of <9% in all cases. Analyses with the present HPLC method show significant differences (p<0.05) in losartan MRs between the four CYP2C9 genotype groups in 13 Spanish healthy volunteers.
  
  
  CONCLUSIONS
  The method developed is simple and affordable, as well as sensitive and reliable to calculate the MR. Therefore, it appears to be useful for CYP2C9 phenotyping using losartan as a drug test in populations, such as Hispanics with different allele combinations.
authors.affiliation: CICAB Clinical Research Centre, Extremadura University Hospital and Medical School, Badajoz, Spain.
authors.forename: Pedro
authors.initials: P
authors.lastname: Dorado
authors.forename: Esther
authors.initials: E
authors.lastname: Machín
authors.forename: Fernando
authors.initials: F
authors.lastname: de Andrés
authors.forename: María-Eugenia
authors.initials: ME
authors.lastname: Naranjo
authors.forename: Eva M
authors.initials: EM
authors.lastname: Peñas-Lledó
authors.forename: Adrián
authors.initials: A
authors.lastname: Llerena
mesh_terms: D000328:Adult; D000959:Antihypertensive Agents / Q000652:urine*; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics*; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D065729:Cytochrome P-450 CYP2C9; D005260:Female; D005838:Genotype; D006801:Humans; D006900:Hydroxylation; D007093:Imidazoles / Q000652:urine*; D019808:Losartan / Q000652:urine*; D008297:Male; D008875:Middle Aged; D010641:Phenotype; D013777:Tetrazoles / Q000652:urine*
chemical_list: D000959:Antihypertensive Agents; D007093:Imidazoles; D013777:Tetrazoles; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; C066026:losartan carboxylic acid; D019808:Losartan