Pharmacogenetic Tests

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What is pharmacogenetics?

We don’t all respond to the same drugs in the same way. Sometimes a drug will work for one person and not for another, or may cause different side-effects in different people. Our individual responses can be due to the genes we have inherited. With respect to drugs, our unique genetic make-up and our individual characteristics may mean that a drug that is effective for one person is less effective for another, or that a drug that is safe for one person may be dangerous for another person—even at the same dose.

Most drugs are broken down (metabolized) in the body by various enzymes. In some cases, an active drug is made inactive (or less active) through metabolism. In other cases, an inactive (or less active) drug is made more active through metabolism. The challenge in drug therapy is to make sure that the active form of a drug stays present just long enough to do its job. However, some people have enzymes that don’t work in quite the same way as other people, and they may metabolize the drug too quickly or too slowly or not at all — meaning that it may be gone before it has its intended effect, or it may hang around for too long and build up beyond safe levels, leading to side-effects.

A person’s response to a drug may also be related to variation in the drug target – for example, a protein that the drug binds to in order to produce its particular effect. Also, individuals may experience severe side effects (known as hypersensitivity reactions) from some drugs due to variations in the proteins involved in the body’s immune response.

Pharmacogenomics is the study of genetic variability that causes individual responses to medications. By analyzing the genes that are linked to the specific drug targets or the enzymes that metabolize a drug that is to be prescribed, a doctor may decide to raise or lower the dose, or even to use a different drug. The decision about which drug to prescribe may also be influenced by other drugs the patient is taking, to avoid interactions between drugs.

The terms “pharmacogenetics” and “pharmacogenomics” are sometimes used interchangeably. There are subtle differences between the two terms, and no consensus on their exact definitions. In general, pharmacogenomics refers to the overall study of the various genes that contribute to drug response, while pharmacogenetics is the study and evaluation of the inherited difference that affect an individual’s response to drugs.The term pharmacogenetics will be used in this article.

Why is pharmacogenetics important?

When starting a patient on a drug to treat a particular condition, doctors typically prescribe one of several appropriate drugs The dose and timing are usually based on the rate of metabolism and clearance from the body in the average person. They begin by prescribing a “standard” dose based on factors such as weight, sex, and age, and then adjust the dose or change the drug over time, depending on whether the patient’s condition is responding to the medication and whether the patient is experiencing unpleasant or dangerous side effects. Sometimes, a patient may find that a treatment that has been working well for them suddenly does not work so well or causes side-effects when they start taking an additional drug.

The concentrations of some drugs are monitored with blood tests and the dosages increased or decreased to maintain the drug level in an established “therapeutic” range. Follow-up in this way is called “Therapeutic Drug Monitoring” . If changing the drug dose is not effective in treating or controlling the patient’s condition, or side-effects persist, then the patient is given a different drug and the process is started again.

In contrast to this rather empirical approach, pharmacogenetics is now beginning to offer doctors the opportunity to individualizs drug therapy for patients based on their genetic make-up and get the dosage right from the start. Testing people before treatment is initiated to determine the way in which they will respond to certain classes of drugs is an important emerging area of laboratory testing. This genetic information could help both the doctor and the patient when choosing current and future drugs and doses. For certain drugs, pharmacogenetic testing is already helping doctors predetermine drugs and doses that have the best chance of achieving the desired therapeutic effect while reducing the likelihood of adverse effects.

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