Pharmacogenetics Testing, Drug Response Testing or Pharmacogenetics

Dr Din and Pima Neurology offer PharmacoGenetic Testing.
Several pharmacogenetic tests have been developed, representing tangible deliverables of the numerous genomic studies to correlate genetic variation with variable drug response. A handful of these tests, both protein- and DNA-based, have subsequently been approved.

Pharmacogenetic (PGx) testing is a type of genetic test that assesses a patient’s risk of an adverse response or likelihood to respond to a given drug, informing drug selection and dosing. 1 As a pillar of the personalized medicine movement, PGx testing is anticipated to be important across all medical specialties, 2 but particularly in primary care, where the majority of all drug prescriptions are written.3 It has been estimated that many of the drugs commonly prescribed by primary care practitioners (PCPs) such as fluoxetine, metoprolol, warfarin, and simvastatin are affected by PGx variation. 45 Although several different strategies of delivering PGx testing have been proposed or are being investigated, 68 at present, there is little clarity on which health professionals should order PGx testing, at what stage during treatment testing should be ordered, how best to communicate results to patients, and where results should be stored to inform future therapeutic decision making. 9 Patients prefer receiving PGx test results from a familiar provider whom they trust such as a PCP; 910 however, several factors have contributed to the slow integration of PGx testing in the primary care setting, 1112 including limited time as well as familiarity and experience with PGx testing.1315 Because PGx testing is a relatively new field and many PCPs are unfamiliar with many of the basic tenets of the field, ongoing learning opportunities and/or faculty development would enable PCPs to feel more comfortable with the topic, and presumably engage in more effective communication with patients, and more appropriate use of testing. This paper suggests key elements to be discussed with patients prior to testing and when reporting test results to assist PCPs while recognizing some of the practical limitations in the primary care setting.

The purpose of PGx testing is to determine the risk of side effects and/or likelihood of effectiveness of a given medication.1 Physicians are often asked about side effects of prescribed drugs and factors that may alter the effectiveness of a drug, and if PGx testing is an option, it should be part of that conversation. In particular, PCPs can point out that a small change in a gene important in metabolizing or transporting (or other function) occurs in a subset of patients and a test is available to detect this change. The physician should briefly describe the possible outcomes regarding adjusting dose or drug selection based on the test result. Details such as gene name, specific variation, or gene function would be unnecessary.

It should be emphasized that identification of a genetic change or metabolic activity does not necessarily indicate an absolute diagnosis of non-response or that a side effect will or will not occur upon use of a given drug. The scientific basis of the role of genes in drug response is incomplete and rapidly changing and other factors may affect drug response. In addition, although the physical risks are no greater than for any other clinical test, it should be mentioned that federal law31 prohibits any use of genetic information by health insurers and employers, though other groups may still use this information (eg, life insurers and the military). Another issue PCPs may face is patient confusion as a “normal” PGx test result doesn’t necessarily mean the patient is not at risk for adverse events or non-response because current tests only capture known variants in known genes. Additionally, other factors such as cost of testing, insurance coverage, and risk of delay of treatment while waiting for testing to be completed may influence the patient’s decision to have testing. If the patient declines to have testing, the PCP should discuss alternative interventions to limit risk of side effects or non-response as medically warranted. For example, initial dose selection can be minimized, dose escalations can be modest, a review of concomitant drugs for potential drug–drug interactions can be conducted, and selection of alternate drugs in the same class that are less susceptible to PGx interactions may be considered.