Stereoselective metabolism of metoprolol in Caucasians and Nigerians--relationship to debrisoquine oxidation phenotype.

The relationship between debrisoquine oxidation phenotype and the stereoselective metabolism of metoprolol was investigated in populations of British Caucasians (n = 139) and Nigerian subjects (n = 117). The 0-8 h urinary S/R-metoprolol (S/R-M) ratio was related to the ability to metabolise metoprolol and debrisoquine in both ethnic groups. The median S/R-M ratio was significantly higher in Caucasians (1.27) than in Nigerians (1.10). In the Caucasian population poor metabolisers of debrisoquine had significantly lower S/R-M ratio (median = 0.84) than extensive metabolisers (median = 1.28). Bimodality in the frequency distribution of the S/R-M ratio was not apparent in either ethnic group.