Dextromethorphan polymorphic hepatic oxidation (CYP2D6) in healthy black American adult subjects

The objective of this study was to assign metabolizer phenotype to 107 healthy adult black Americans using dextromethorphan as the substrate probe. Eligible subjects were unrelated, healthy, nonsmoking, aged 18-50 years, and taking no medications. Fifteen milliliters of dextromethorphan syrup (85 mumol, 30 mg) was administered orally at bedtime, and 8-h overnight urine was collected. Dextromethorphan and dextrorphan urinary areas and molar ratios were determined using high-performance liquid chromatography with fluorescence detection. A molar metabolic ratio of < 0.3 was used to segregate poor metabolizers (PM) from extensive metabolizers (EM). Data were obtained in 99 subjects: 68 women, 31 men. (Five were lost to follow-up, three did not take the probe drug.) Six (6.1%) were PM (five women, one man), and 93 were EM. The prevalence of PM was 6.1% (95% confidence interval, 2.3-12.7%) in our sample. This compares to 5 to 10% reported in white unrelated subjects and 1.9% in 106 black children (64 healthy and 42 with cancer), and 0-8.6% in black African populations. The clinical implications of these findings warrant further investigation.