Pharmacogenomics or pharmacogenetics is the study of how a person's genes affect how they respond to medicines. It is a relationship doctors have been investigating for years, and only now are they growing closer to being able to tailor drugs and dosages to individual patients.

The medicines you take rely on internal mechanisms to metabolize and transport them throughout your body. During this process, thousands of protein molecules interact with them and may alter how well they work. This means that your genes may affect how effectively (or ineffectively) you absorb and metabolize a particular drug, which in turn affects how well the drug works for you.

Therefore, your genetic make-up could alter your response to drugs used to manage all types of conditions, including depression, pain, blood pressure, and more. It also explains why, in some cases, you may need to try several different medicines to find the one that works for you.

While medicines may work well for most people, in certain people, a medicine may not work or it may cause annoying side effects. In some cases, these genetic-drug mismatches can prove fatal. Knowing a patient’s genetic code may, therefore, someday help doctors make drug treatments safer.

Multiple studies have demonstrated the correlation between genes and drug response. The National Institute of General Medical Sciences, a part of the National Institutes of Health (NIH), has funded extensive research in this area. The basic link between genetics and drug efficacy is clear, but more research is needed to reach a practical understanding of how to apply knowledge to everyday care.

Cancer drugs have been an area of particular interest. This is because in cancer care the need to know whether a drug will or will not work is vitally important, both because these drugs often produce serious side effects and because the time it takes to prove a drug ineffective may allow cancer cells to grow or metastasize.

One example of the importance of genetics in cancer care is how the thiopurine methyltransferase (TPMT) gene affects the way some people metabolize a certain class of drug used to treat leukemia. Some children who are treated with this class of drug have an alteration in the TPMT gene that causes their bodies to metabolize the drug very slowly. When these children are given the standard dose of medicines in this class, the medicines can build up in their bodies, reaching potentially toxic levels. Other children, however, metabolize this class of drug much more rapidly. These children require larger doses to benefit from the drug. Fortunately, a blood test can determine how long it will take a child to process the drug, and the dose can be adjusted in advance.

Within the next several years, your doctor may be able to tailor your treatment according to your genetic make-up. Some laboratories offer blood tests to check for gene alterations that vary the effect of cancer drugs. These tests are designed to look for specific changes that may affect the drug about to be ordered. In the future, it may get even easier.

In the end, the experts offer patients some suggestions for learning more about these issues and technologies:

• Ask if any information about genes and drugs exists for your condition.
• Stay aware of new developments.