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