Introduction
The purpose of this evidence review is to examine genetic testing used to inform drug therapies and determine if the evidence is sufficient to draw conclusions about better health outcomes for the Medicare population. Generally, key health outcomes include patient survival and disease incidence, along with quality of life and daily functioning. A standardized assessment of analytical validity, clinical validity, and clinical utility should be thoroughly explained and should indicate the confidence level that the test's performance will directly benefit patients. Tests that prove analytical and clinical validity, along with demonstrated clinical utility that inspires confidence in enhancing clinician decision-making, have the potential to change clinical management and improve patient outcomes. Optimal patient outcomes show reduced mortality and morbidity, as well as enhanced quality of life and functionality.
Pharmacogenomic (PGx) testing aims to enhance patient outcomes by optimizing medication selection, thus minimizing ineffective medication use and reducing adverse events. The desired outcomes remain the same patient-centered results mentioned above.
Internal Technology Assessment
The U.S. sources of PGx test recommendations available to provide guidance to clinicians as to how available genetic test results should be interpreted for drug therapy improvement include the U.S. FDA drug labels, FDA Table of Pharmacogenetic Associations, and the CPIC.
Hertz 2024
This narrative review article investigates the current status of PGx testing recommendations within clinical practice guidelines (CPGs) in the United States. The authors aim to understand how PGx testing is integrated into these guidelines, focusing on 21 gene-drug pairs that are recognized as clinically actionable by CPIC¹.
The methodology involved a targeted review of CPGs from U.S.-based clinical organizations. The selection of guidelines was informed by subject matter experts in various therapeutic areas, ensuring that the most prominent guidelines for each gene-drug pair were included. Although a systematic search for all possible CPGs was not conducted due to practical challenges, the review focused on those guidelines that explicitly discussed PGx testing. The article does not involve new clinical trials or participant recruitment but rather synthesizes existing guidelines and the evidence they present.
The authors identified inconsistencies both within and between organizations regarding PGx testing recommendations, particularly in how different guidelines approach the same gene-drug pairs. For instance, while some guidelines consistently recommend testing, such as HLA-B*57:01 before abacavir therapy, others show variability, like those for CYP2C19 with clopidogrel. This variability underscores the need for a more standardized approach to evaluating the clinical utility of PGx testing¹.
In conclusion, the article calls for more consistent inclusion of PGx testing recommendations in CPGs, suggesting that such consistency could enhance clinical adoption of PGx testing and ultimately improve patient outcomes. The review highlights the importance of a standardized methodology for evaluating the evidence that supports these recommendations, which could help align guidelines across different clinical organizations¹.
Morris 2022
The systematic review analyzed 108 studies evaluating the cost-effectiveness of PGx testing for drugs with CPIC guidelines. The review found that 71% of these studies demonstrated PGx-guided treatment to be either cost-effective (44%) or cost-saving (27%), with the majority of these studies (87%) being of high quality as indicated by a Quality of Health Economic Studies (QHES) score of 75 or higher. Specifically, the drugs clopidogrel and warfarin were the most studied, with 96% of clopidogrel-related studies showing cost-effectiveness or cost-saving outcomes². In contrast, only 44% of warfarin studies showed cost-effectiveness, with none reporting cost savings².
Moreover, the review highlighted that the majority of studies (69%) were based on hypothetical populations, and most were conducted in North America (47%) and Europe (24%)². The findings underscore that while PGx testing is generally considered cost-effective or cost-saving, there are significant variations depending on the drug, gene, and study design. Additionally, studies from Asia were more likely to report PGx testing as not cost-effective (36%), suggesting geographical and methodological factors may influence cost-effectiveness outcomes². This variability emphasizes the need for region-specific evaluations when considering the adoption of PGx testing in clinical practice².
Caudle 2016
This study addresses the slow integration of pharmacogenetics into clinical practice despite considerable scientific advancements. One significant barrier is the uncertainty around the necessary evidence threshold for applying genetic test results to patient care. Large randomized controlled trials (RCTs) are often impractical or unnecessary for many pharmacogenetic applications, particularly when robust mechanistic evidence exists³. The authors note that, in many cases, clinical decisions can be made based on pharmacokinetic studies and other forms of evidence without requiring extensive RCTs³.
The study highlights the crucial role of resources like CPIC and the Pharmacogenomics Knowledgebase (PharmGKB). These platforms provide evidence-based guidelines that help clinicians translate genetic test results into actionable prescribing recommendations³. By offering standardized approaches to evaluate the literature, CPIC and PharmGKB facilitate the application of pharmacogenetic knowledge in clinical settings, ensuring that genetic information is used effectively in patient care³.
A key component of the study is the discussion of CPIC's level system, detailed in a table below. The CPIC levels range from A to D, categorizing the strength of evidence and recommendations for using genetic information in prescribing decisions³. Level A represents the highest confidence, where genetic information should be used to alter prescribing, while Level D indicates insufficient evidence or conflicting data, suggesting no need for action³. This classification system helps clinicians make informed decisions about when and how to incorporate pharmacogenetic data into their practice³.
In conclusion, the study underscores the importance of standardized guidelines and evidence-based resources in advancing the implementation of pharmacogenetics in clinical practice³. By using tools like CPIC and PharmGKB, clinicians can navigate the complexities of genetic data, making informed decisions that enhance patient outcomes³. The transparent and dynamic nature of these guidelines allows for continuous refinement as new evidence emerges, supporting the broader integration of precision medicine into healthcare³. CPIC levels of evidence for genes and drugs, Table 1:
Table 1. CPIC Level Definitions for Genes and Drugs
CPIC Level
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Clinical Context
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Level of Evidence
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Strength of Recommendation
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A
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Genetic information should be used to change prescribing of affected drug
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Preponderance of evidence is high or moderate in favor of changing prescribing
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At least one moderate or strong action (change in prescribing) recommended
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B
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Genetic information could be used to change prescribing of the affected drug because alternative therapies/dosing are extremely likely to be as effective and as safe as non-genetically based dosing
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Preponderance of evidence is weak with little conflicting data
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At least one optional action (change in prescribing) is recommended
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C
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There are published studies at varying levels of evidence, some with mechanistic rationale, but no prescribing actions are recommended because (a) dosing based on genetics makes no convincing difference or (b) alternatives are unclear, possibly less effective, more toxic, or otherwise impractical or (c) few published studies or mostly weak evidence and clinical actions are unclear. Most important for genes that are subject of other CPIC guidelines or genes that are commonly included in clinical or DTC tests.
|
Evidence levels can vary
|
No prescribing actions are recommended
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D
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There are few published studies, clinical actions are unclear, little mechanistic basis, mostly weak evidence, or substantial conflicting data. If the genes are not widely tested for clinically, evaluations are not needed.
|
Evidence levels can vary
|
No prescribing actions are recommended
|
Caudle 2014
This article reviews the development and implementation of CPIC guidelines, which are designed to integrate pharmacogenomic data into clinical practice. The authors provide an overview of the CPIC guideline development process, highlighting the systematic approach used to translate genetic test results into actionable prescribing decisions4. The review compares this process with the Institute of Medicine’s (IOM) standards for developing trustworthy CPGs, emphasizing areas of alignment and opportunities for improvement4.
The CPIC guidelines focus on well-established gene-drug pairs with strong evidence linking genetic variations to drug response4. Each guideline follows a standardized format that includes a rigorous review of scientific literature, grading of evidence, and assignment of the strength of recommendations4. The guidelines are designed to help clinicians interpret patient-specific genetic information and apply it to optimize drug therapy, without advising on whether genetic testing should be conducted4.
The article identifies several key challenges and considerations in the guideline development process, such as managing conflicts of interest and ensuring transparency4. The authors also discuss the importance of electronic health records (EHRs) and clinical decision support (CDS) systems in facilitating the use of CPIC guidelines in clinical settings4. To this end, efforts are being made to enhance the machine-readability of these guidelines, enabling seamless integration with EHRs4.
In conclusion, the authors emphasize the critical role of CPIC guidelines in advancing the clinical adoption of pharmacogenomics4. They call for continued efforts to refine the guideline development process, address existing challenges, and expand the reach of these guidelines to improve patient outcomes4.
U.S. Food and Drug Administration (FDA)
The FDA describes pharmacogenetic testing as a critical tool in personalizing medical treatment by identifying patients who are likely to respond well or poorly to specific medications5. This testing helps to avoid adverse drug reactions and optimizes drug dosing by taking into account individual genetic variations5. Pharmacogenomic information is integrated into drug labeling and may provide insights into the variability of drug exposure and clinical responses, the risk of adverse events, and the need for genotype-specific dosing5. Additionally, it can inform the mechanisms of drug action, highlight polymorphic drug target and disposition genes, and guide trial design features5.
The FDA's approach to pharmacogenomic information in drug labeling is nuanced, allowing for its inclusion in various sections depending on the specific actions required based on the biomarker data5. This information may pertain to germline or somatic gene variants, functional deficiencies with a genetic origin, gene expression differences, and chromosomal abnormalities5. Selected protein biomarkers that play a role in treatment decisions are also included5. However, the FDA excludes non-human genetic biomarkers, those used exclusively for diagnostic purposes unrelated to drug activity, and biomarkers linked to drugs other than the one in question5.
The FDA recognizes the significant advancements and potential benefits of genetic testing, particularly in informing individuals about their health risks and guiding medical decisions6. Direct-to-consumer genetic tests are becoming increasingly popular among consumers seeking insights into their ancestry or disease risks, while healthcare providers use genetic testing to tailor patient care6. Pharmacogenetics, a field exploring the role of genetics in drug response, is particularly promising, with some drugs like clopidogrel (Plavix) having established links between genetic variants and drug efficacy6. However, the FDA warns against the use of pharmacogenetic tests that have not undergone FDA review, as they may lack the necessary scientific and clinical evidence to support their claims, potentially leading to harmful changes in patient treatment6.
The FDA is particularly concerned about unapproved genetic tests marketed directly to consumers or offered through healthcare providers that claim to predict a patient's response to specific medications6. Such tests may inaccurately suggest changes in drug treatment based on unsubstantiated genetic links, posing serious health risks6.
In 2018, the FDA issued a warning regarding the use of genetic tests that claim to predict a patient's response to specific medications, emphasizing that many of these tests lack FDA review and scientific support7. The agency is concerned that such tests, which may be marketed directly to consumers or through healthcare providers, could lead to inappropriate treatment decisions and potentially serious health consequences7. For instance, some tests claim to determine the effectiveness of antidepressants based on genetic variations, but the FDA has found no established link between DNA variations and the efficacy of these medications7. The agency advises patients and healthcare providers not to alter medication regimens based on the results of unverified genetic tests7.
In 2023, the FDA issued a draft guidance intended for industry stakeholders involved in drug development and aims to provide updated recommendations on the submission of pharmacogenomic data to the FDA8. The agency's expectations for pharmacogenomic data submissions in drug development are centered on four key themes: relevance to drug safety and efficacy, level of detail in reporting, integration into regulatory processes, and standardization of data formats8.
The FDA emphasized the importance of submitting pharmacogenomic data that is directly relevant to understanding a drug's safety profile or efficacy8. This includes findings that indicate substantial differences in treatment response across genomic subgroups, identify significant safety risks in certain populations, or relate to the drug's mechanism of action or pharmacokinetics8. The agency requires detailed reports for genomic biomarkers used in clinical trial design or analysis, and expects sponsors to submit data on biomarkers proposed for inclusion in drug labeling8. This focus on relevance ensures that the submitted pharmacogenomic information contributes meaningfully to the overall evaluation of the drug's benefits and risks8.