Pharmacogenomic Testing (PGx)

Genetic variants play a significant role in an individual’s ability to metabolize and respond to medications, impacting both efficacy and toxicity. Pharmacogenomic testing evaluates a patient’s response to a specific drug prior to prescribing, providing information about expected efficacy or the risk of side effects.

What is Pharmacogenomics?

The term "pharmacogenomics" describes how genetic variants affect drug metabolism and response. Cytochrome P450 (CYP) enzymes and drug receptors may have common variants that influence the metabolism rate of many commonly prescribed medications. Individuals are classified as "poor metabolizers," "intermediate metabolizers," "extensive (normal) metabolizers," or "ultra-rapid metabolizers" based on their CYP variants. Poor and ultra-rapid metabolizers may require different dosages or face a higher risk of side effects.

Table 1. Examples of Medications Affected by Common Genetic Variants

Impact of Genetic Variants on Drug Metabolism

Genetic variants can affect:

• Pharmacokinetics: Genetic variants in metabolizing enzymes can influence how the body processes drugs.
• Pharmacodynamics: The drug’s effect on the body is influenced by genetic variants at drug targets (e.g., receptors).

Pharmacogenomic testing analyzes genes involved in these two processes. For example, the cytochrome P450 family produces enzymes involved in drug metabolism. P450 enzymes account for 70–80% of enzymes involved in drug metabolism. Common variants in P450 genes can affect the function of the enzymes produced, thereby impacting the metabolism of certain medications.

Genetic variants result in four different phenotypes regarding drug response:

• Poor metabolizers have significantly reduced or no enzyme activity.
• Intermediate metabolizers have reduced enzyme activity.
• Extensive (normal) metabolizers have normal enzyme activity.
• Ultra-rapid metabolizers have elevated enzyme activity.

Codeine Recommendations Based on Metabolizer Status

Benefits of Pharmacogenomics

The benefits of pharmacogenomic testing stem from its ability to tailor medications to individuals: specifically, predicting the correct dose to avoid toxicity or side effects and determining whether a specific drug is likely to be effective in a particular patient.

Benefits of pharmacogenomics include:

• Achieving optimal drug dosage quickly – avoids the trial-and-error approach associated with repeated monitoring.
• Minimizing toxicity and side effects – a patient’s genetic profile can help reduce the likelihood of adverse outcomes and guide clinicians to suitable alternatives.
• Effective drug use – genetic variants can predict which patients are likely to respond to certain medications, enabling clinicians to personalize treatment.
• Evidence is accumulating from randomized controlled trials on some of these benefits for specific applications of pharmacogenomic testing (e.g., antidepressants).

Pharmacogenomic testing may be considered for patients who:

• Experience significant side effects from medications with known pharmacogenomic variability in response (see Table 1).
• Have a poor therapeutic response to specific medications.
• Are likely candidates for doses outside the usual range.

System Used: GeneTitan System (ThermoFisher Scientific)

• PGx Testing (Pharmacogenomics)
• Kits Used: PharmacoScan, PharmacoFocus, PMDA, PangenomiX
• Purpose: Analyzes genetic variants related to drug response, aiding in personalized treatment.

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