Preemptive genotyping is a process for determining the genetic make-up of patients before prescribing medication that may cause adverse reactions according to specific markers in their genes. Adoption of this technique has been slow to rise, but the screening can only benefit patients. According to the International Congress of Human Genetics in Montreal last month, 30% of cardiologists and 41% of primary care providers agreed to free genetic testing after prescribing clopidogrel (a medication known to have adverse effects in a small number of patients). Though testing was done after prescribing clopidogrel, results helped determine the relationship between genetic markers and patient reaction to clopidogrel which can be of use later.
“Eventually, genetic information will be available in all patients, and part of making that a clinical reality is helping the health system know what to do with that information,” said University of Florida Gainesville pharmacotherapy expert, Julie Johnson.
One instance in which the utility of preemptive genotyping was demonstrated was during a hospital implementation of preemptive genotyping by Vanderbilt University. In 2010, Vanderbilt University Medical Center launched the Pharmacogenomic Resource for Enhanced Decisions in Care and Treatment or PREDICT for short. The PREDICT system uses genetic markers and patient medical history to predict what drug therapies and dosages would best suit a patient. In an ongoing clinical trial, the PREDICT system has been applied to dealing with whether or not patients requiring heart catheterizations should be given clopidogrel (required during heart catheterizations). So far, more than 3000 ‘cath lab’ or catheterization laboratory patients received genetic tests. Of these, about 700 patients were flagged for genetic variations with the potential for an adverse reaction from clopidogrel. These patients received alternative medications.
As interventional cardiologist John McPherson recalls, one patient was flagged to likely be a poor metabolizer of clopidogrel because of a faulty yet vital liver enzyme, so he prescribed the patient Effient (prasugrel) instead. The patient was found faring well six months later. As Dr. McPherson says, ”If he wasn’t part of this trial, most likely he would have been placed on clopidogrel because that’s what we do, and who knows what would have happened to him.”
