Effective use of pharmacogenomics in primary care

With the increasing trends of prescription drug use and polypharmacy in the US,^1,2 prescription decisions continue to be a major aspect of the primary care provider role. 

While trial-and-error and titration (adjusting medication to find the optimal dose) have been the standard approach to choosing and prescribing drugs, it is by definition an inexact process. Medications are typically developed, marketed, and prescribed based on data generated from clinical trials, approved by the US FDA. Approvals are usually a compilation of the data to determine the use of the medication in an average patient. However, no two patients are alike—and the “error” aspect of a trial-and-error prescribing strategy may result in a negative outcome. 

Advances in genetic testing provide tools—such as pharmacogenomics (PGx)—to determine whether a patient’s genetic profile may affect the efficacy and side-effect profile of a particular medication.

This personalized information can help clinicians tailor therapies to support safer, more effective prescribing decisions. Due to their role in prescribing medications, primary care providers are in a position to help patients benefit from the information yielded through PGx testing.³

In this article:

Clinical challenge | Why it matters | Ordering recommendations | Interpreting test results | Next steps | Supporting resources

Clinical challenge: Improving confidence in prescribing antidepressants, anticoagulants, statins, and other chronic disease drug therapies

In recent years, total prescription medicine use in the US has increased, reaching 210 billion days of therapy in 2025.¹ Recent data show that 68% of Americans report taking at least one prescription medication daily.²

In addition, polypharmacy is increasing significantly,⁴ with 26% of US adults reporting they take 4+ prescriptions per day.²

Polypharmacy can be especially elevated in people with chronic conditions such as heart disease and diabetes.⁴ In addition, mental health and polypharmacy tend to be closely linked, because psychiatric medications—in many cases prescribed as multi-drug regimens—are often added to treatments for chronic illness.⁵

Prescribing standardized medications to a variety of patient types drives the need for individualized information

Pharmaceutical companies design standard doses and formulations that are statistically safe and effective for a broad population—relying on clinicians to use labeling and dose variations to adjust for individual responses to a drug. 

As a result, many patients on the same prescription drug may experience less efficacy or more side effects [Figure 1].⁶

For patients taking multiple medications, this variability is multiplied, increasing the potential likelihood of adverse drug events.⁷

Multiple factors affect medication response 

When prescribing drugs, it’s important to consider all factors, both extrinsic and intrinsic: 

The intrinsic factor of genetics provides the opportunity to add valuable individualized information to a patient’s clinical profile. This makes it a significant factor to consider—preemptively—when making prescription decisions.

Why it matters: Genetic variations can impact drug efficacy and response, including ADRs 

A recent study found that adverse drug reactions (ADRs) account for an estimated 5% of hospital admissions.⁸

Additionally, the high incidence of polypharmacy can lead to an increased risk of adverse drug interactions (ADIs).⁵ This underscores the need for medication strategies more precise than trial-and-error prescribing and titration.

Pharmacogenomic (PGx) testing can add significant and lasting pieces to the clinical puzzle of individual patient response

PGx testing utilizes patient-specific genomic markers to assist clinicians in the selection of medications with the highest likelihood of success while minimizing the risk of toxicity. 

Research has shown that PGx testing can reduce the risk of ADRs, with a recent European study finding that PGx-guided dosing can reduce ADRs by 30%.⁹

In fact, PGx guideline recommendations are available for many of the drugs often implicated in ADRs, including warfarin, antiplatelet agents, and opioid analgesics.^{10, 11}

In addition, PGx guidelines are available for several drugs and drug categories commonly used in primary care, including certain antidepressants, statins, analgesics, antibiotics, and contraceptives.¹⁰

Pharmacogenetics presents an opportunity for safer and more efficient pharmacotherapy—minimizing trial-and-error prescribing and supporting better outcomes.¹²

The connection between genetics, patients, and prescriptions

PGx testing has been shown to reduce adverse drug events in a specific HIV medicine, as well as certain medications used in cardiology and oncology

Examples include:

HIV – Abacavir is indicated for HIV infection treatment and used as part of some highly active antiretroviral therapy regimens. However, patients with the HLA-B*57:01 allele are at risk for severe, potentially life-threatening hypersensitivity reactions.¹⁴

To reduce the risk of these adverse reactions, drug labeling for abacavir recommends that all patients should be screened for the HLA-B*57:01 allele before initiating or reinitiating abacavir, unless the patient has been previously tested.¹⁴

Cardiology – In a large-scale national clinical study, genotype-guided dosing of warfarin reduced the rate of hospitalizations by 31% in outpatients initiating warfarin.¹⁵

Oncology – Fluoropyrimidine-based chemotherapy is a frequently prescribed class of anticancer drugs. A prospective study reported that genotype-guided dosing of the fluoropyrimidine therapy was associated with significantly reduced toxicity, risk of drug-induced death, and treatment costs.¹⁶

Genetic insights from PGx testing provide lasting clinical value

Because PGx testing analyzes germline DNA, the results remain valid for life.¹⁷ As medication regimens evolve, the information provided can support safer prescribing decisions at every stage of care. Combined with clinical judgment and patient-specific factors (eg, age, comorbidities, or concurrent therapies), PGx testing provides a foundation for more informed, personalized treatment.

Ordering recommendations: Specialized PGx panels to analyze genes known to influence drug metabolism

Quest offers 2 PGx panels to analyze 21 genes tied to clinically actionable gene-drug associations, supported by evidence from expert groups like the Clinical Pharmacogenetics Implementation Consortium (CPIC) and ClinPGx. 

While both panels analyze the same 21 genes, each produces a different reporting structure:

Pharmacogenomics Panel

• Generates a Quest-delivered report with genotype (diplotype) and predicted phenotypic response*
• Does not provide medication guidance but enables the prescribing HCP to follow up with their own sources of information for specific PGx results

Pharmacogenomics Panel with Coriell Life Sciences

• Generates a Quest-delivered report with genotype (diplotype) and predicted phenotypic response*
• Provides medication guidance to a personalized report powered by InformedDNA^®, based on current gene-drug evidence. Offering lifetime access via a protected link, this dynamic report is updated as relevant new gene-drug evidence becomes available

* For medication-specific guidance based on these findings, test code 14271 (Pharmacogenomics Panel with medication guidance from Coriell) includes access to a Coriell Life Sciences enhanced report that incorporates drug-gene interaction guidance from curated sources such as CPIC®. Quest does not review or validate Coriell reports. These are developed independently by Coriell's professional staff. Test code 14272 (Pharmacogenomics Panel) does not contain this guidance from Coriell.

These PGx panels can help inform decisions across a broad range of clinical areas in a single test.

When to consider PGx testing

PGx testing provides insight into whether a patient is a normal, poor, intermediate, rapid, or ultrarapid metabolizer. These panels can provide helpful information to guide drug-related decisions such as selection and dosage in treatment contexts including 

• Before initiating medications
• When a patient experiences adverse effects or poor response to a medication
• When therapeutic targets are not met despite dose adjustments
• When assessing genetic impact across multiple therapeutics in polypharmacy patients

Recommended tests: Polypharmacy PGx panel with medication guidance

Pharmacogenomics panels analyze genes tied to clinically actionable, high-evidence gene-drug associations.

Pharmacogenomics Panel

• Test code: 14272 (Pharmacogenomics Panel)
• CPT^® code: 81418

Pharmacogenomics Panel with Coriell Life Sciences (CLS) Report

• Test code: 14271 (Pharmacogenomics Panel with medication guidance from Coriell)
• CPT code: 81418

Note: When test code 14271 (Pharmacogenomics Panel with medication guidance from Coriell) is ordered, a link to obtain a comprehensive gene-drug interaction report from Coriell Life Sciences will be available at no additional cost. Information provided by Coriell may be updated as new information becomes available. Providers can access updated information through the provided link using Coriell’s GeneDose live software. If test code 14271 (Pharmacogenomics Panel with medication guidance from Coriell) is not ordered, no link will be available. It will not be possible to obtain medication guidance from Coriell at a later date after results for 14272 Pharmacogenomics Panel without medication guidance are provided. In such a case, the ordering HCP must determine the PGx effects through other sources of information.  

Interpreting test results: Applying PGx test results to more individualized prescription decisions

Results across both pharmacogenomics panels include genotype (diplotype) and predicted phenotypes.

Normal Metabolizer (NM)

This result indicates that a patient is likely to break down medications through this genetic pathway normally and thus is likely to achieve expected drug response at standard doses.

Intermediate Metabolizer (IM), Poor Metabolizer (PM)

Patients with IM or PM results may metabolize some medications more slowly than NM patients and may experience reduced effectiveness or unwanted side effects.

Rapid Metabolizer (RM), Ultrarapid Metabolizer (UM)

RM or UM results suggest a patient may process drugs more quickly, which can reduce therapeutic efficacy or increase side effects. 

In addition to genes that code for drug-metabolizing enzymes, the panels include other genes that may influence medication response.

Next steps: Evaluating current medications and adjusting prescription decisions 

After receiving PGx panel results, recommendations include reviewing the patient’s current medication list, interpreting the genes with actionable prescribing guidance, and adjusting or avoiding medications in alignment with clinically relevant findings.¹⁸

Implementing changes based on panel results can also involve a pharmacist and/or genomics specialist when possible.