Pharmacogenomics Offers a Glimpse Into the Future of Pharmacy

In the quickly advancing science and health care fields, pharmacogenomics (PGx) is a growing asset to pharmacy and health care. In the near future, it will be essential to include PGx testing to benefit all of our patients.

PGx is essentially the science of getting the right drug for the right patient at the right dose and time, and it works to reduce the trial-and-error method of prescribing. We have the knowledge and capabilities to be more precise with our prescribing habits, and in the future, we should utilize PGx test results like we utilize creatine clearance for dosing vancomycin.

For several therapeutic categories of medications, we prescribe a guideline-based initial dose and/or medication. For example, if a patient is prescribed warfarin for atrial fibrillation, we typically start that patient on 5 mg (sometimes 2.5 mg) and ask that they return for an International Normalized Ratio blood test. If that patient possesses a CYP2C9*2 or CYP2C9*3 variant, a pharmacist needs to step in to recommend a lower initial dose.¹ This is largely due to the reduced metabolism of warfarin that is observed with this genetic variant, which leads to an increased risk of a bleeding event.

After providing that lower dose, pharmacists ask the patient to follow up with their prescriber in the coming months to ensure that they have an adequate response. Thanks to their close patient relationships and accessibility, pharmacists are the ideal health care providers to make the transition from “one-size-fits-all” prescribing to providing the right dose for the right patient. Pharmacists are capable of using their pharmacy training to interpret PGx test results and create an action plan moving forward.

Utilizing PGx testing unveils the patient’s reaction to a medication, demystifying the process and helping provide more effective care sooner rather than later. PGx results inform practitioners as to whether a medication will work and which dose of the medication is required, and it can reduce the adverse effect profiles with appropriate dosing. At its core, PGx is the concept of personalizing a patient’s medication regimen to optimize their health outcomes.

Another example that arises in psychology is the use of paroxetine and the variants within the CYP2D6 gene. For patients that are CYP2D6 ultra-rapid metabolizers, avoiding paroxetine completely and initiating another selective serotonin reuptake inhibitor not metabolized by CYP2D6 is recommended.²

As more guideline recommendations surface thanks to research, we will have more opportunities to implement PGx changes moving forward. Ultimately, PGx testing reduces the number of visits to practitioners’ offices, cuts down on the number of failed medications, and prevents adverse events by providing a more accurate dose.

PGx involves delivering a PGx test to a patient, which can often be completed in their home. In some instances, depending on the state the pharmacist practices in and the lab that the pharmacist is working with, the pharmacist can order the lab work themselves. Once the lab receives the order, they deliver the test to the patient. The patient swabs the inside of their cheek and sends the package back to the lab for processing. Once processing is complete, the results are delivered to the pharmacist for evaluation, and the pharmacist compares the patient’s medication list with the metabolism levels of particular enzymes associated with their medications.

The reports are quite extensive and will state whether a patient is an ultra-rapid metabolizer, an extensive metabolizer, an intermediate metabolizer, or a poor metabolizer. Depending on the lab that performed the testing, the report will state whether the results are actionable or essentially informational. This is largely due to whether the finding relates to a PGx guideline that exists or not. Once the pharmacist reviews the results, they can discuss them with the patient’s prescriber to offer some recommendations based on the findings.

As a pharmacy student, there are several things you can do to keep yourself updated with the changes in PGx. First and foremost, if you notice a medication metabolized by CYP enzymes, ask yourself whether the patient is being adequately treated and the desired outcome is achieved. CYP enzymes are discussed quite frequently due to the genetic variability that is common among patients.

You can also familiarize yourself with the Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines and the information constantly being updated on their website to assist pharmacists and prescribers. As a recent student, I believe it is important to have difficult conversations with prescribers to make changes to current practices. PGx is one of the topics that many health care providers shy away from because they do not know enough about it, but pharmacists have the knowledge and capabilities to provide answers for prescribers and patients.

ABOUT THE AUTHOR

Matthew Busalacchi, PharmD, is a recent graduate of the University of Iowa College of Pharmacy and a graduate of the University of Wisconsin with a bachelor's degree in genetics. With a background in community and hospital pharmacy, he is pursuing a long-term career in pharmacogenomics.

REFERENCES

1. Giacomini KM, Yee SW, Ratain MJ, Weinshilboum RM, Kamatani N, Nakamura Y. Pharmacogenomics and patient care: one size does not fit all. Sci Transl Med. 2012;4(153):153ps18. doi:10.1126/scitranslmed.3003471

2. Hicks JK, Bishop JR, Sangkuhl K, et al. Clinical Pharmacogenetics Implementation Consortium (CPIC) guideline for CYP2D6 and CYP2C19 genotypes and dosing of selective serotonin reuptake inhibitors. Clin Pharmacol Ther. 2015;98(2):127-134. doi:10.1002/cpt.147