title: Use of omeprazole sulfone in a single plasma sample as a probe for CYP3A4.
abstract: OBJECTIVE
  The hydroxylation of omeprazole, measured as the ratio of omeprazole/5-hydroxyomeprazole in a plasma sample taken 3 h after an oral dose, is an established method to determine CYP2C19 activity, and the ratio of omeprazole AUC/omeprazole sulfone AUC has been used for assessing CYP3A4 activity. The aim of this study was to determine whether the latter ratio from a single 3-h sample can also be used for CYP3A4 phenotyping.
  
  
  METHODS
  Plasma levels of omeprazole and omeprazole sulfone were analyzed by reversed-phase high-performance liquid chromatography in a blood sample drawn 3 h after intake of a single oral 20-mg dose of omeprazole by 22 healthy subjects and five patients with newly diagnosed epilepsy. The procedure was repeated on the 4th day of 200 mg of ketoconazole intake (10 subjects), after 3 weeks of 150-200 mg twice-daily carbamazepine (five patients), and on the 6th day of 4 mg twice-daily tolterodine (12 subjects). Five subjects also took 100 mg and 50 mg of ketoconazole for 3 days before concomitant intake with omeprazole.
  
  
  RESULTS
  The mean log10(omeprazole/omeprazole sulfone) ratio was 0.18 3 h after intake of omeprazole alone. After concomitant intake of ketoconazole, the corresponding value was 1.38 (p<0.001); after intake of carbamazepine it was -0.42 (p<0.05); and after tolterodine it was 0.29 (not significant). In the five subjects taking increasing doses of ketoconazole, the ratio was 0.11, 0.79, 1.2, and 1.5 after 0, 50, 100, and 200 mg of ketoconazole, respectively. The correlation between the metabolic ratios from the AUC((0-6h)) and from the single 3-h samples was very good, with a correlation coefficient of 0.92 (p<0.001).
  
  
  CONCLUSIONS
  A single blood sample taken 3 h after intake of 20 mg of omeprazole can be reliably used to phenotype for both CYP2C19 and CYP3A4 activity.
authors.affiliation: Division of Clinical Pharmacology, Department of Laboratory Medicine, Karolinska Institutet, Karolinska University Hospital, 141 86 Stockholm, Sweden. ylva.bottiger@ki.se
authors.forename: Ylva
authors.initials: Y
authors.lastname: Böttiger
mesh_terms: D000328:Adult; D000368:Aged; D001189:Aryl Hydrocarbon Hydroxylases / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D002220:Carbamazepine / Q000494:pharmacology*; D002851:Chromatography, High Pressure Liquid; D065731:Cytochrome P-450 CYP2C19; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D004347:Drug Interactions; D020536:Enzyme Activators / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D006801:Humans; D007654:Ketoconazole / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged; D006899:Mixed Function Oxygenases / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D009853:Omeprazole / Q000031:analogs & derivatives* / Q000097:blood* / Q000493:pharmacokinetics / Q000494:pharmacology; D010597:Pharmacogenetics
chemical_list: D020536:Enzyme Activators; D004791:Enzyme Inhibitors; D002220:Carbamazepine; C040450:omeprazole sulfone; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C045793:CYP2C19 protein, human; D065731:Cytochrome P-450 CYP2C19; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D009853:Omeprazole; D007654:Ketoconazole