I heard it’s possible now to have a blood test to see if a certain drug will work before taking it. This seems like a good idea before spending so much money on a prescription that doesn’t work. What’s the name of the test?

You may be referring to a blood test that allows genetic analysis to predict and monitor drug effects. The process of choosing the right drug using the best dosage is called pharmacogenomics. Pharmacogenomics is based on a genetic analysis of each condition and each patient. It is still in its infancy stages of development.

Researchers are indeed trying to find ways to predict what drug to choose for each patient based on their genetics. But this practice is not routine yet. Most of the research is in the area of cancer drugs. For example, doctors are trying to avoid using chemotherapy on patients if it’s not going to help. Tests are being developed to tell ahead of time if it will or won’t work for each type of cancer.

In general, we do know there are many factors that affect how a drug is used or metabolized by each individual person. Age, sex, overall health, and even hydration (how much fluid is in the body) can all affect how well the body can break down and use the active chemicals in a drug.

And scientists have discovered certain enzymes that also help (or hinder) the process. For example, an enzyme called cytochrome P450 2D6 (or CYP2D6 for short) has been shown to help metabolize opioid (narcotic) drugs. Any genetic mutation, defect, or duplication of that gene can change the way the body metabolizes the drug.

So far, it looks like people fall into one of four categories. They may be ultrarapid metabolizers. This occurs because they have multiple copies of CYP2D6. They may be poor metabolizers. This means there is no detectable activity of the enzyme. Or they may fall somewhere in between with decreased or poor enzymatic activity.

In the future, pharmacogenomics including genetic analysis will become a routine part of each medical exam. This type of testing may be available if you are being treated in an area where there is a rapid response laboratory or medical research facility.

Without this type of testing, patients and physicians will still have to use the trial and error method of finding the best dose of the right medication for each patient, condition, or disease.