CYP2D6 phenotype prediction from genotype: which system is the best?

Genotyping of the polymorphic cytochrome P450 (CYP) 2D6 gene is used increasingly in clinical practice. Several psychiatric hospitals already use CYP2D6 testing before treating a patient with antidepressant or antipsychotic drug therapy. In other fields of drug therapy, such as for breast cancer, CYP2D6 status has been reported to be an independent predictor for the outcome with tamoxifen. Thus, a more favorable tamoxifen treatment seems to be feasible through a priori genetic assessment of CYP2D6.