Personalized medicine is based on the realization that people react in individual ways to drug treatments based on their unique genetic makeup and metabolism. It has been estimated that drug treatments are only effective in about 60% of patients, while other patients either show no response or have a detrimental response to the drugs. This lack of effectiveness represents losses of billions of dollars.
The Basis for Personalized Medicine
The individual's response to drug treatments is largely based on genetics. Genes consist of specific sections of the DNA molecule that contain instructions for the synthesis of a protein. These sections contain chemical structures called nucleotide bases. Polymorphism, "many forms," is due to differences in the nucleotide sequence of genes, giving rise to alleles. These differences, in turn, lead to differences in the proteins that are synthesized. Single nucleotide polymorphisms, or SNPs, are the most common type. (Olle) Over 660 SNPs have been identified that effect over 100 diseases.
Individuals can differ greatly in their response to drugs. Drugs may need to be metabolized to an active form, they need to be transported to the location where they exert their effect, an active receptor must bring them into the cell, and finally, the drug must be excreted to prevent a toxic buildup of the drug. All of these activities are governed by genes. The study of how the individual's genetic inheritance affects drug response in the body has been termed pharmacogenomics.
Applying Personalized Medicine Through Genetic Testing
The completion of the Human Genome Project allowed the possibility of analyzing the entire genome of a patient. This is not feasible nor necessary. Genetic testing can focus on susceptible individuals based on family history. When drug usage is associated with ineffective or toxic responses, tests should be developed to screen patients for SNPs in drug response genes. A few examples of these tests are as follows.
A group of enzymes known as cytochrome P450 (CYP450) enzymes are responsible for metabolizing more than 30 types of drugs. Other drugs are metabolized through the CYP2D6 or The CYP2C9 enzymes.Tests for these enzymes can be used to determine dosing and the effect of certain antidepressant medications, anticoagulants, acid reflux inhibitors, and other medications.
Coumadin (warfarin) is used to treat cardiovascular disease. Polymorphisms in four genes can lead to excessive bleeding, buildup of toxic doses, tissue necrosis, and other adverse effects.
Herceptin has been shown to be effective in breast cancer patients whose tumors overexpress the HER-2 gene. However, only about 20-25 percent of breast cancer patients overexpress this gene, so pre-testing is needed.
Recent Progress in Personalized Medicine
A non-governmental organization called the Personalized Medicine Coalition has been established that draws from a large cross section of organizations including industry, academics, and health care professionals. ( Leavitt) The FDA has also taken a prominent role in encouraging (and in some cases even requiring) genetic testing of patients.
Large pharmaceutical companies have been slow in developing the personalized medicine model, since it could have the potential of reducing profits from blockbuster drugs. Recent entrants onto the scene include Medco Health Solutions and CVS Caremark, representing retail pharmacies. Other companies are sure to follow.
Pharmacogenomics Holds Great Promise
Personalized medicine can be the key to the application of safe and effective medicines. The field is still in its infancy, however, and challenges persist in developing a viable model. (Risher)
Sources:
Jorgensen, J. "From Blockbuster Medicine to Personalized Medicine." Personalized Medicine 2008; 5(1): 55-63
Leavitt M. "Personalized Health Care: Pioneers, Partnerships, Progress." 2008 November. U.S. Dept. of Health and Human Services.
Olle D. "Pharmacogenetics and Cancer Therapy." 2001 December; Suite 101.com
Risher J. "Personalized Medicine." 2008 June; Suite 101.com
David Olle - I have been a freelance writer since 1995, specializing in medicine, science, and nutrition topics. I have been involved in the following ...
