Genetic Testing :
Avoid adverse drug interactions , improve drug efficacy , and prescribe more confidently
Sean Hanlon , Director of Professional Communications Physicians Office Resource
P
ersonalized medicine offers the promise of optimizing drug therapy for each , individual patient . Since collectively , our bodies , organs , enzymes and genes are all unique , not all patients respond appropriately to a standard , one-size-fits-all approach to drug therapy . A single DNA test provides a lifetime of knowledge about a patient ’ s drug sensitivity and rate of drug metabolism , which are central to optimizing drug selection and thereby protecting against drug toxicity or reduced efficacy .
Genetic tests of the P450 cytochrome system have become available through specialty laboratories over the past decade , with acceptance first seen in the cardiology community . New this year , however , CMS has added new codes to the Physician Fee Schedule , facilitating 100 % coverage for some of these tests . Many of the private insurers have followed suit and also reimburse for these tests , effectively broadening the availability of this tool for physicians and patients .
Given the wide-ranging applicability of this test , we thought we would provide a brief overview for our readers this month . More information is available by searching # 7922 at www . physiciansofficeresource . com .
Background
The vast majority of drugs are metabolized through the liver and the P450 cytochrome system of drug metabolizing enzymes ( DMEs ). This includes CYP2C9 , CYP2C19 , CYP2D6 , CYP3A4 and CYP1A2 . In fact , the P450 system metabolizes over 50 % of today ’ s most commonly prescribed drugs .
The function of one or more of these DMEs can be affected by gene variants . Patients with gene variants ( 5 % -45 % depending on ethnicity ) are more likely to experience drug toxicity or lack of efficacy because the altered enzyme function can change the rate at which the liver metabolizes drugs . Most variants cause a loss of enzyme function and patients with reduced enzyme function are poor or intermediate metabolizers . Fewer people have variants that increase enzyme function and these patients are rapid or ultra-rapid metabolizers . And , of course , many people have a normal drug metabolism profile .
Clinical Utility & Rationale
The P450 cytochrome pathway is well known in the cardiology community , with leading institutions , such as Scripps , Vanderbilt , the Mayo Clinic and others incorporating routine testing for variations of the C2YP19 gene . In particular , for patients on or candidates for blood thinner therapy , Vanderbilt “ believes the real utility of this strategy will be in the outpatient setting ”, performing the test well in advance of the patient needing an antiplatelet agent .
A recent study by Medco and the Mayo Clinic showed that ordering a P450 cytochrome-related test early – prior to starting therapy – reduces hospitalization rates by nearly 1 / 3 rd for patients on blood thinners . This is critically important because patients on blood thinners have the highest incidence of adverse
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