Individualized pharmacotherapy: background and development.

Most drug prescriptions are still based on empiricism and not on solid biological data, which often results in considerable patient variability and, sometimes, low patient benefits. Although variability in patient response to pharmacotherapy has long been recognized, only in recent decades have new molecule analytical methods provided insight into some of the causes, which are often related to somatic or germline genetic variations. Based on this insight, different predictive biomarker tests have been developed to optimize and individualize pharmacotherapy. These biomarker tests are classified as companion diagnostic (CDx) or pharmacogenetic (PGx) tests. In both the United States and Europe, CDx and PGx information is part of the regulatory drug labeling and is included in the Prescribing Information for the individual drugs and biologics. In the United States, this type of information is found in the labeling of more than 400 regulatory-approved drugs and biological products. Despite these measures and the documented clinical utility of CDx and PGx testing, clinical implementation is lagging, especially with regard to PGx. There are various reasons for the lack of testing, such as insufficient education and awareness among healthcare professionals, inadequate access to biomarker testing, regulatory hurdles, and insufficient reimbursements. Although progress has been made in recent years, further efforts are needed to fully realize the potential of individualized pharmacotherapy by integrating the use of predictive biomarkers into routine clinical practice.