Video: When to Consider Pharmacogenomic Testing for Your Patient
Pharmaceuticals are prescribed with the assumption that they will provide some benefit to the patient, and will do so safely. Unfortunately, that is not always the case. Commonly used pharmaceuticals are rarely efficacious in everybody. Efficacy varies by drug class, with cancer therapies and Alzheimer's disease drugs on the lower end of the spectrum (Fig. 6-1). Similarly, pharmaceuticals are not always safe in everybody. Rare and severe adverse events occur in 1–2% of patients (a conservative estimate) and are found across many different therapeutic areas.
The application of pharmacogenomics (also called pharmacogenetics) refers to using a patient's genetic information to improve the efficacy and/or reduce the side effects of drugs. Some drugs are only effective in patients with a certain genetic biomarker, in which case a pharmacogenomic test for that biomarker is essential prior to prescribing the drug. This is the case for most of the targeted treatments developed in cancer (reviewed in Chapter 8) and for the cystic fibrosis drugs ivacaftor and lumacaftor/ivacaftor. In other cases the efficacy of a drug may be improved by using a pharmacogenomic test that guides appropriate dosing of the drug. Toxicity-based biomarkers are those that are used to identify people likely to experience side effects when taking the drug. Side effects can range from rare life-threatening adverse events to less severe outcomes. Some toxicities can be avoided by either avoiding the drug or adjusting the dose of the drug based on pharmacogenomic tests that reveal the patient's potential to metabolize the drug.
Efficacy of commonly used classes of therapeutics. (Adapted with permission from Spear BB, Heath-Chiozzi M, Huff J: Clinical application of pharmacogenetics, Trends Mol Med. 2001 May;7(5):201-204).
WHEN TO ORDER A PHARMACOGENOMIC TEST
It is estimated that >98% of people in the United States have at least one actionable pharmacogenomic variant from among the 12 most common pharmacogenomic tests, yet most don't know it. That's all changing as several health care institutions (Mayo Clinic, Mt. Sinai Medical Center, St. Judes Children's Research Hospital, University of Florida and Shands Hospital, Vanderbilt University Medical Center) have begun to implement preemptive pharmacogenomic testing programs, making pharmacogenomic information available in the patient medical record prior to any prescribing decision. Preemptive testing will become increasingly common, but until then, when prescribing a drug where there is a known pharmacogenomic association health care providers must decide whether to order a pharmacogenomic test.
There are 138 drugs with pharmacogenomic information in the U.S. Food and Drug Administration (FDA) label (http://www.fda.gov/drugs/science-research/researchareas/pharmacogenetics/ucm083378.htm), the majority (40%) of which are for oncology drugs and discussed in Chapter ...