Pharmacogenomics Basics for Pharmacy Technicians

What Is Pharmacogenomics?

Pharmacogenomics (PGx) studies how a person's genetic makeup affects their response to medications. Variations in genes that encode drug-metabolizing enzymes, transporters, and receptors can make a patient a poor metabolizer, intermediate metabolizer, extensive (normal) metabolizer, or ultra-rapid metabolizer of specific drugs. This information helps prescribers choose the right drug and dose for each patient.

Key Enzymes in Pharmacogenomics

The cytochrome P450 (CYP) enzyme family is central to pharmacogenomics:

• CYP2D6 - Metabolizes codeine, tramadol, tamoxifen, and many antidepressants. Ultra-rapid metabolizers convert codeine to morphine too quickly, risking toxicity. Poor metabolizers get no pain relief from codeine.
• CYP2C19 - Metabolizes clopidogrel (Plavix), omeprazole, and certain antidepressants. Poor metabolizers may not activate clopidogrel, reducing its antiplatelet effect.
• CYP2C9 and VKORC1 - Together these genes influence warfarin dosing. Variants can increase bleeding risk or reduce warfarin effectiveness.

Clinical Applications

Pharmacogenomic testing is now common before starting certain drugs:

• Abacavir - HLA-B*5701 testing is required before starting this HIV drug to prevent severe hypersensitivity reactions.
• Carbamazepine - HLA-B*1502 testing is recommended in patients of Asian descent to prevent Stevens-Johnson syndrome.
• Fluoropyrimidines (5-FU, capecitabine) - DPYD testing identifies patients at risk for severe toxicity.

The Technician's Role

While technicians do not interpret PGx results, they encounter them in practice. PGx test results may be flagged in the patient profile, and certain prescriptions may include notes about metabolizer status. Understanding the basics helps you process these orders accurately and communicate with pharmacists effectively.

Pharmacogenomics is an emerging area that strengthens your understanding of pharmacology concepts tested on the PTCE.