Polymorphism of dextromethorphan oxidation in South Indian subjects

One hundred fifty-six unrelated healthy South Indian subjects were phenotyp ed according to their ability to metabolize dextromethorphan to its O-demet hylated metabolite dextrorphan, Each volunteer was administered 25 mg oral dextromethorphan hydrobromide (19.3 mg dextromethorphan). Urine was collect ed during an 8-hour period after drug administration and was analyzed for d extromethorphan and dextrorphan by HPLC with fluorescence detection. This a nalysis was performed with and without previous deconjugation. The log(10) (metabolic ratio), calculated as the ratio of dextromethorphan to dextrorph an, was bimodally distributed, and it was inferred that the frequency of oc currence of poor metabolizers of dextromethorphan in South Indian subjects is 3.2%, Phenotype assignment remained the same with both methods of analys is. Furthermore, a fairly good correlation (Spearman rank order correlation coefficient [r(s)] = 0.61; P <.0001) was observed between the log-transfor med metabolic ratio derived from both methods.