When pharmaceutical companies develop new drugs for any given disease state, they are limited by a lack of knowledge about how individual patients will respond to the agent. No simple algorithms exist that facilitate prediction of whether a patient will respond negatively (an adverse drug reaction), positively (the desired outcome), or not at all. Consequently, drugs are developed for an "average" patient. The manufacturer relies on clinical studies to expose potential adverse reactions and publishes them in statistical format to guide the physician. Nevertheless, when a physician prescribes a drug to a patient he or she has no way of knowing the outcome. Statistics show clearly that a single drug does not provide a positive outcome in all patients. This "one-drug-does-not-fit-all" concept has its basis in the genetics of a patient, and the science of studying these phenomena is called pharmacogenomics.
A patient's response to a drug, positive or negative, is a highly complex trait that may be influenced by the activities of many different genes. ADME, as well as the receptor-binding relationship, are all under the control of proteins, lipids, and carbohydrates, which are in turn under the control of the patient's genes. When the fact that a person's genes display small variations in their DNA base content was recognized, genetic prediction of response to drugs or infectious microbes became possible. Pharmacogenomics is the science that looks at the inherited variations in genes that dictate drug response and tries to define the ways in which these variations can be used to predict if a patient will have a positive response to a drug, an adverse one, or none at all.
Cataloging the genetic variations is an important phase of present research activity. Scientists look for SNPs in a person's gene sequences. SNPs are viewed as markers for slight genomic variation. Unfortunately, traditional gene sequencing is slow and expensive, preventing for now the general use of SNPs as diagnostic tools. DNA microarrays may make it possible to identify SNPs quickly in a patient's cells. SNP screening may help to determine a response to a drug before it is prescribed. Obviously, this would be a tremendous tool for the physician.
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