Genetic Testing Underutilized for Cardiovascular Therapy

Patients treated with an antiplatelet drug, who have loss-of-function alleles for a specific gene, have an increased risk for adverse cardiovascular events if they are poor metabolizers of the drug.

Scientists at Brigham and Women's Hospital (Boston, MA, USA) assessed the impact of Cytochrome P450, Family 2, Subfamily C, Polypeptide 19 (CYP2C19) genetic testing on prescribing patterns for antiplatelet therapy among patients with acute coronary syndrome or percutaneous coronary intervention. For the study, the doctors of the patients were offered access to a genetic test for CYP2C19 in order to determine their patients' abilities to metabolize clopidogrel. This drug is thienopyridine class antiplatelet agent. Some of the patients were also offered the genetic testing directly. Genotype and phenotype results were provided to patients and their physicians, but no specific treatment recommendations were suggested.

Almost 500 patients completed the test, while prescribers declined genetic testing in 25% of all cases. Less than 10% of patients declined the test when offered it directly. Of the 500 patients who had the testing, one-third were found to be poor metabolizers of drugs. However, the study findings revealed that although patients who had this genetic testing were more likely to have their prescription of clopidogrel changed, compared with patients who did not have the genetic test, only 20.5% of poor metabolizers were swapped to another drug or had their antiplatelet therapy boosted.

Between July 2010 and April 2012, 6,032 patients were identified, and 499 (8.3%) underwent CYP2C19 genotyping, of whom 146 (30%) were found to have greater than or equal to one reduced function allele, including 15 (3%) with two reduced function alleles. Although reduced function allele carriers were significantly more likely than noncarriers to have an intensification of their antiplatelet therapy, only 20% of poor metabolizers of clopidogrel had their antiplatelet therapy intensified.

Niteesh K. Choudhry, MD, PhD, the senior author of the study said, “While there is significant uncertainty about how clinicians should respond to the results of genetic testing for antiplatelet drugs, this study clearly shows that patients and their doctors need more guidance and education about how best to apply these results to improve patient outcomes.” The study was published on November 5, 2013, in the journal Circulation: Cardiovascular Quality and Outcomes.

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