Researchers in the field of pharmacogenomics study genes that produce drug-metabolizing enzymes in the body. Utilizing an individual's genetic profile in prescribing medications for various diseases will prevent unwanted side-effects and allow drugs to work more efficiently. Pharmacogenomics requires the analysis of an individual's genetic information and the comparison of that genetic information, along with reactions to specific drugs, to the information and reactions of others to determine which drugs most effectively treat a given disease or condition. Although pharmacogenomics is not yet widely used, this technology is likely to someday change the way physicians practice medicine and the expectations of patients in seeking treatment. (2)      The way a person responds to a drug (this includes both positive and negative reactions) is a complex trait that is influenced by many different genes. Without knowing all of the genes involved in drug response, scientists have found it difficult to develop genetic tests that could predict a person's response to a particular drug. Once scientists discovered that people's genes show small variations in their nucleotide (DNA base) content, all of that changed—genetic testing for predicting drug response is now possible. Pharmacogenomics is a science that examines the inherited variations in genes that dictate drug response and explores the ways these variations can be used to predict whether a patient will have a good response to a drug, a bad response to a drug, or no response at all. (4)

     This understanding of the genetic variations in drug response opens the door to "personalized medicine" by (1) identifying patients who are more prone to experience adverse events from a drug and (2) identifying patients who are more likely to benefit from a particular therapy. This information has the potential to guide the selection of a drug for a particular patient and to tailor the drug dose to achieve the optimal therapeutic effect. In addition, knowledge of the genetic makeup of infectious agents is being used to guide treatment. For example, the identification of the specific drug resistance mutations in a patient's human immunodeficiency virus (HIV) is used to select the therapy most suitable or best "targeted" for that patient. In these ways, pharmacogenomics has the potential to assist physicians in adapting drug treatments to the characteristics of individual patients, ultimately leading to safer and more effective prescribing and dosing. (8)