What is the likelihood of a patient being a poor metabolizer or an ultra-rapid metabolizer?
While patients generally can be classified into one of four phenotypic groups, there is pronounced ethnic and geographic variability, with some polymorphisms and alleles found in virtually only one racial population. Approximately 7% of Caucasians are poor metabolizers of CYP2D6, whereas only about 1% to 2% of Asian and 2% to 4% of African American populations are in that same category. There is a 50% prevalence of several reduced-activity alleles in Asians and a 30% prevalence in certain African populations that lead to a higher percentage of intermediate metabolizers with low enzyme activity. Although the extreme activities of the poor and ultra-rapid metabolizer phenotypes have the greatest potential effect on individual drug response, intermediate metabolizers have also been shown to respond differently to certain drugs.
