Evaluation of a [13C]-dextromethorphan breath test to assess CYP2D6 phenotype

J Clin Pharmacol. 2008 Sep;48(9):1041-51. doi: 10.1177/0091270008319709.


A [(13)C]-dextromethorphan ([(13)C]-DM) breath test was evaluated to assess its feasibility as a rapid, phenotyping assay for CYP2D6 activity. [(13)C]-DM (0.5 mg/kg) was administered orally with water or potassium bicarbonate-sodium bicarbonate to 30 adult Caucasian volunteers (n=1 each): CYP2D6 poor metabolizers (2 null alleles; PM-0) and extensive metabolizers with 1 (EM-1) or 2 functional alleles (EM-2). CYP2D6 phenotype was determined by (13)CO(2) enrichment measured by infrared spectrometry (delta-over-baseline [DOB] value) in expired breath samples collected before and up to 240 minutes after [(13)C]-DM ingestion and by 4-hour urinary metabolite ratio. The PM-0 group was readily distinguishable from either EM group by both the breath test and urinary metabolite ratio. Using a single point determination of phenotype at 40 minutes and defining PMs as subjects with a DOB <or=0.5, the sensitivity of the method was 100%; specificity was 95% with 95% accuracy and resulted in the misclassification of 1 EM-1 individual as a PM. Modification of the initial protocol (timing of potassium bicarbonate-sodium bicarbonate administration relative to dose) yielded comparable results, but there was a tendency toward increased DOB values. Although further development is required, these studies suggest that the [(13)C]-DM breath test offers promise as a rapid, minimally invasive phenotyping assay for CYP2D6 activity.

Publication types

  • Evaluation Study
  • Research Support, N.I.H., Extramural

MeSH terms

  • Administration, Oral
  • Adult
  • Breath Tests / methods*
  • Carbon Dioxide / metabolism*
  • Carbon Isotopes
  • Cytochrome P-450 CYP2D6 / genetics
  • Cytochrome P-450 CYP2D6 / metabolism*
  • Dextromethorphan / administration & dosage
  • Dextromethorphan / pharmacokinetics*
  • Feasibility Studies
  • Female
  • Genotype
  • Humans
  • Kinetics
  • Male
  • Middle Aged
  • Phenotype
  • Predictive Value of Tests
  • Sensitivity and Specificity
  • Young Adult


  • Carbon Isotopes
  • Carbon Dioxide
  • Dextromethorphan
  • Cytochrome P-450 CYP2D6