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Genetic Tests for Drug Sensitivity: What Exactly is Precision Medicine?

It just doesn’t seem to make sense. There’s this new medication that seems to be a “wonder drug” for a friend or some member of your family. Everybody is talking about it. You have the same symptoms, so you get a prescription and take the medicine. Nothing happens. Nothing. Or, you take a medicine prescribed to help you and your partner relax and get a good night’s sleep. Instead, it’s you starting a fresh batch of cookies at three in the morning and binge-watching old episodes of “Seinfeld”. Meanwhile, cuddly bear is snoring soundly in bed. How is that even possible?? The answer, of course, lies in science and, like so many of life’s complexities, you can blame the genes that you were born with. As my Mom used to say, “You can’t choose your parents.” Nor, Mom, can you choose your DNA. Like brunette or blonde, blue eyes or brown, tall or short, thick or thin, our genetic structure drives it all, and the ambiguity in our individual response to medicine is no different. Who we are, what we look like, and how our bodies respond to the substances we ingest is all written and directed by our DNA. Want to learn more? “Pharma” means “drug”. “Genome” means, well, “genome”. “Pharmacogenomics” is the scientific study of how our genetic traits influence our unique response to different medications. Drop that one at the dinner table some evening. But, here’s what’s really disappointing: despite the explosive growth of knowledge around pharmacogenomics over the past decade, and the ability to custom tailor medications to each patient, most practitioners persist in the “one-size-fits-all” approach to medication therapy that completely ignores individual differences. And it has been clearly shown, for various common conditions like depression, pain, high blood pressure, and cancer that have been heavily studied, utilizing this trial-and-error approach causes as many as 75% of patients to experience suboptimal responses to drug therapy. That leads to wasted health care dollars, critical time lost from productive lives, and unnecessary patient suffering. Pharmacogenomics offers more than just an opportunity for improved therapeutic response, though. Analysis of the genome allows specially trained health care providers further insight into an individual’s particular risks from specific drug therapy. Certain genetic variations cause the body to metabolize a drug more rapidly, potentially leading to a particular medicine being processed out before it has the chance to provide a therapeutic effect. Conversely, another variation might cause the drug to metabolize more slowly, leading to tissue buildup and a greater risk of toxic side effects. Here at ZüpMed, we use a “Drug Sensitivity Test” to predict a patient’s metabolic response to a wide array of medications and pathways. For each of those medications, the patient is labeled:


  • A normal metabolizer who can be expected to have normal or anticipated therapeutic benefit from therapy;

  • An intermediate metabolizer who breaks down medication more slowly and may therefore experience more medication buildup at doses that would otherwise be considered “normal” for others. Depending upon the drug, this can result in less than the expected benefit, or an increased risk for side effects;

  • A poor metabolizer who breaks down medication even more slowly and can experience side effects at even low doses. If unrecognized, toxicity can develop rapidly; or

  • An ultra-rapid metabolizer who quickly breaks down medication with the result that there may not be any therapeutic effect at all. Again, the opposite can occur as well if the drug is of a type that needs to be metabolized in order to become “active”. Too-rapid metabolism sends an unplanned rush of medicine throughout the body, with the potential for disastrous effects.


Thus, understanding your unique genetic profile can help guide practitioners to either increase or reduce standard doses or even to prescribe alternative therapies. It can become even more complex, though. There are often more than one, and even multiple, pathways through which a particular drug must be metabolized in the human body, and thus even more possibilities for numerous genetic alterations to occur along the way. And, just to make things really confusing, each medication added may itself cause interactions or be influenced by a slow or fast metabolic status. Considering all the possibilities, predicting how two or more medications will behave when given together (to say nothing of three, four, five, or more medicines together) is a Herculean task. Fortunately, there are a few pharmacists with specialty training in this area to help interpret the complex results of pharmacogenomic testing. In the right hands, with proper training and experience, “pharmacogenetics” can be used as a clinical tool to make medication therapy both more effective and safer. The goal of this new “Precision Medicine” is to optimize medication therapy so that the maximum efficacy is achieved for each patient while keeping side effects to a minimum. Precision Medicine benefits both the provider and patient by:

  • Shifting the emphasis in prescribing from reaction to prevention

  • Reducing trial and error prescribing

  • Reducing adverse drug reactions

  • Increasing patient adherence to treatment

  • Revealing additional targeted uses for medicines and drug candidates

  • Decreasing unnecessary drug cost.


Over 200 FDA drug labels now contain pharmacogenomic information—including warnings or precautions due to the potential impact of genetic variants on medication efficacy and safety. These warnings by themselves mean little, however, without the clues found in each individual’s genetic profile. Research has shown that proper application of pharmacogenomic information can help patients achieve better response from drug therapy, have fewer treatment failures, are less likely to experience side effects, and are more adherent with personalized treatment plans. Precision Medicine stands clearly at the center of the health care revolution, as science provides us greater ability to treat the right patient at the right time with the right dose of the right medicine. [Dr. Shannon Finks, PharmD, FCCP, BCPS, BCCP, AHSCP-CHC is board certified in Pharmacotherapy and Cardiovascular Pharmacotherapy and has specialty certifications in Applied Pharmacogenomics/Personalized Medicine and Hypertension. She is a Professor at the University of Tennessee College of Pharmacy and oversees comprehensive medication management and Precision Medicine practices at ZüpMed. By partnering with both physicians and patients, she provides consultation and facilitates communication between the patient and providers to achieve optimal therapeutic results.] For more information, contact us or call 901-701-1010.

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