Enzyme polymorphism on the metabolic O-demethylation of dextromethorphan in a South American population.

The polymorphic oxidative metabolism of debrisoquine and sparteine were discovered in the seventies by Mahgoub and Eichelbaum. Since then, many other therapeutic substances were added and one of these drugs is dextromethorphan. The object of this investigation was to ascertain the distribution of the oxidative phenotype of dextromethorphan in the Uruguayan population. The drug and its metabolite, dextrorphan, were quantified in the urine of 165 healthy volunteers by modification of an HPLC method by Chen et al. The metabolic ration was calculated and frequency distribution histograms were drawn. By inspection of the histogram two antimodes can be assigned which determine three sub-populations: on one side the fast extensive metabolizers (n = 30, 18.2%), in the middle the extensive metabolizers (n = 123, 74.5%) and on the other extreme of the histogram the slow metabolizers (n = 12, 7.3%). No other studies have confirmed thus far this trimodal distribution. This research will be continued by genotyping the populations studied in order to confirm these findings and to elucidate the underlying genetic mechanisms of the polymorphism.