title: Stability of the nicotine metabolite ratio in smokers of progressively reduced nicotine content cigarettes.
abstract: BACKGROUND
  The nicotine metabolite ratio (NMR), the ratio of trans-3'-hydroxycotinine (3-HC) to cotinine, has been used as a biomarker of the rate of CYP2A6-mediated nicotine metabolism. While stable in smokers who maintain constant smoking consumption, since smoking has been shown to inhibit nicotine metabolism and this inhibition could be mediated by the nicotine in the smoke, NMR could change during nicotine reduction. The objective of this study was to determine the reproducibility (or stability) of plasma NMR in smokers of progressively reduced nicotine content (RNC) cigarettes.
  
  
  METHODS
  We analyzed data from subjects in a clinical trial of smoking progressively RNC cigarettes. Plasma NMR in 30 smokers whose plasma cotinine levels had decreased by at least 50% from the use of the first test cigarette (12mg nicotine content) to the final test cigarette (1mg nicotine content) was measured on 4 occasions over a period of 24 weeks.
  
  
  RESULTS
  Plasma cotinine and 3-HC decreased by an average of 85% and 84%, respectively, following the use of the first type of RNC cigarette to the last type. Plasma NMR had an average absolute change of 28.5% over the same period. Using repeated measures analysis, changes in plasma NMR over time were not significant with or without controlling for the effects of age, body mass index, gender, and race (p = .24 and p = .23, respectively). The reliability coefficient for repeated measurements of plasma NMR was .72. The average within-subject coefficient of variation for plasma NMR was 21.6% (SD = 12.0%).
  
  
  CONCLUSIONS
  The plasma NMR is relatively stable over time as nicotine levels decline in smokers of progressively RNC cigarettes.
authors.affiliation: Center for Tobacco Control Research and Education, University of California San Francisco, San Francisco, CA;
authors.forename: Gideon
authors.initials: G
authors.lastname: St Helen
authors.forename: Peyton
authors.initials: P
authors.lastname: Jacob
authors.forename: Neal L
authors.initials: NL
authors.lastname: Benowitz
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood; D002140:California; D003367:Cotinine / Q000031:analogs & derivatives* / Q000097:blood*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009538:Nicotine / Q000008:administration & dosage / Q000378:metabolism*; D015203:Reproducibility of Results; D012907:Smoking / Q000378:metabolism*; D062789:Tobacco Products / Q000032:analysis / Q000145:classification*
chemical_list: D015415:Biomarkers; C001381:hydroxycotinine; D009538:Nicotine; D003367:Cotinine