Drug-metabolizing enzymes: Evidence for clinical utility of pharmacogenomic tests

Pharmacogenomic data can facilitate our understanding of the sources of variability in drug response and can potentially lead to improved safety and efficacy of drug therapy for individual patients. Through various initiatives, the FDA is encouraging drug developers to apply the rapidly evolving pharmacogenomic tools and integrate these data into the evaluation of patient variability. The FDA has clarified when these data are required submissions and when they are exploratory data that can be shared via a newly established process (voluntary genomic submission). Increasingly, pharmacogenetics and genomic information are being included in drug labeling before market approval (eg, trastuzumab [Herceptin; Genentech Inc, South San Francisco, Calif], atomoxetine [Strattera], and voriconazole [Vfend]) or after approval, when new information becomes available (eg, thioridazine [Mellaril], 6-mercaptopurine [Purinethol], and irinotecan [Camptosar]), so that health care providers and patients have updated information on how genomics, along with other factors (age, gender, hepatic, renal impairment, concomitant medications, and others), can influence individual responses. Various genomic tests are being developed for use with the previously mentioned or other drug products. For example, a recently approved chip provides genotyping of CYP2D6 and CYP2C19. Another test was approved to provide genotyping of UGT1A1. There are many challenges to the effective translation of pharmacogenomic information to clinical practice, and they need to be addressed before the full potential of pharmacogenomics to optimize patient therapy can be realized. This commentary addresses one of the critical issues in the collection of pharmacogenomic data. Defining what basic polymorphic alleles to evaluate in various ethnic or racial groups is important for common, known valid metabolic biomarkers such as CYP2D6, CYP2C9, CYP2C19, and UGT1A1 (Table III). It is also timely to discuss emerging data for exploratory biomarkers (eg, CYP3A4/3A5, ABCB1, or methods involving tagging SNPs) because their correlations with clinical response have been increasingly evaluated during drug development. Other clear challenges include the following: education of health care providers and patients, insurance coverage of pharmacogenomic tests, the availability of robust and valid tests, and the need for an interdisciplinary counseling team approach to address complex issues with individual patients. Many individuals and organizations are working to remove these barriers to full use of pharmacogenomics to improve public health. Copyright © 2005 by the American Society for Clinical Pharmacology and Therapeutics.