Evaluation of a [13C]-dextromethorphan breath test to assess CYP2D6 phenotype.
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.
Leeder
J Steven
JS
Section of Developmental Pharmacology and Experimental Therapeutics, Department of Pediatrics, Children's Mercy Hospitals and Clinics, 2401 Gillham Road, Kansas City, MO 64108, USA. sleeder@cmh.edu
Pearce
Robin E
RE
Gaedigk
Andrea
A
Modak
Anil
A
Rosen
David I
DI
D000284:Administration, Oral; D000328:Adult; D001944:Breath Tests / Q000379:methods*; D002245:Carbon Dioxide / Q000378:metabolism*; D002247:Carbon Isotopes; D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics / Q000378:metabolism*; D003915:Dextromethorphan / Q000008:administration & dosage / Q000493:pharmacokinetics*; D005240:Feasibility Studies; D005260:Female; D005838:Genotype; D006801:Humans; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D010641:Phenotype; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D055815:Young Adult
D002247:Carbon Isotopes; D002245:Carbon Dioxide; D003915:Dextromethorphan; D019389:Cytochrome P-450 CYP2D6