By knowing a patient's disposition to specific drugs, a physician should, ideally, be able to start their patient on an appropriate regimen from day one rather than trying to perfect the dose using trial and error. While PGx testing may help with this goal, the many other factors that affect drug disposition have prevented PGx from being a widely used tool for dosing drugs. However, specific assessments of alleles that are known to be associated with toxicity are being tested more and more. These include alleles like HLA 15:02, HLA 57:01, TPMT, etc. In these cases, adverse drug reactions are avoided by testing, and second-line therapies metabolized by different, unaffected enzymes can be chosen. CYP450 testing will likely continue to be developed into more useful clinical algorithms. Dosing recommendations for PM, EM, IM, and UM patients are beginning to appear in the literature for various classes of drugs, and the FDA is encouraging the incorporation of pharmacogenomic testing in the development process for new drugs. Testing for other alleles related to toxicity (non-CYP450 genes like the HLAs mentioned on the previous page) is certainly becoming the standard of care.
