LC-MS/MS analysis of dextromethorphan metabolism in human saliva and urine to determine CYP2D6 phenotype and individual variability in N-demethylation and glucuronidation

In order to establish a fast screening method for the determination of the CYP2D6 metabolic phenotype a sensitive LC-MS/MS assay to quantify dextromethorphan (DEX) and its O-demethylated metabolite dextrorphan (DOR) in human saliva was developed with limits of quantitation of 1 pmol/ml. Saliva was provided by 170 medical students 2 h after oral ingestion of 30 mg (81 mumol) dextromethorphan hydrobromide. Individual ratios of the concentrations DEX/DOR (metabolic ratio, MRDEX/DOR) varied more than 25,000-fold (0.03-780). Two groups comprising 156 'Extensive' and 14 'Poor Metabolizers' were clearly distinguished. For the investigation of individual differences in N-demethylation and glucuronidation, four additional metabolites of DEX, 3-methoxymorphinan (MOM), 3-hydroxymorphinan (HOM), and the two O-glucuronides (DORGlu and HOMGlu) were measured by LC-MS/MS analysis of 6-h urine of 24 volunteers. The N-demethylation reactions DEX-to-MOM and DOR-to-HOM defined by the respective MR were significantly correlated. The same holds for the glucuronidation pathways (MRDOR/DORGlu). Versus MRHOM/HOMGlu)- The three poor CYP2D6 metabolizers excreted relatively high amounts of the parent compound DEX (up to 7 mumol), but only low amounts of glucuronides (DORGlu: 0.4-1.0 mumol; HOMGlu: 0.2-0.7 mumol). For the 21 'Extensive Metabolizers', the two glucuronides were the most abundant, with relatively little interindividual variation (DORGlu: 10-44 mumol; HOMGlu: 5-17 mumol). For the excretion of the glucuronides, two normal distributions provided the best fit, indicating that the determination of the glucuronides alone could allow assignment of the CYP2D6 metabolic phenotype. (C) 2004 Elsevier B.V. All rights reserved.