Assessment of the Implementation of Pharmacogenomic Testing in a Pediatric Tertiary Care Setting

Key Points Question What is the clinical utility of a pharmacogenomic testing program that uses both point-of-care and preemptive approaches to assess potential responses to drugs in a pediatric tertiary care setting? Findings In this cohort study of 172 pediatric patients, pharmacogenomic testing of 6 pharmacogenes (CYP2D6, CYP2C9, CYP2C19, CYP3A5, TPMT, and VKORC1) provided results that warranted deviation from standard treatment regimens in approximately 40% of patients in the point-of-care evaluation of targeted drugs and 80% of patients in the preemptive evaluation of a broader range of drugs for potential therapy. Meaning The study’s findings suggest that a pharmacogenomic program using both point-of-care targeted drug–guided testing and preemptive whole-genome sequencing–guided testing enhances the knowledge necessary for patient care decision-making, providing informed rationales for drug selection and dosing options.


Introduction
Monitoring the efficacy and safety of medications prescribed to children is of substantial importance, especially in a tertiary care setting, in which patients typically have complex medical conditions that often require treatment with multiple medications.A study conducted among 1 million Canadian children found that only 20% of children accounted for 70% of all drug prescriptions. 1 Those children were more likely to be diagnosed with chronic health conditions that required treatment in advanced care settings 1 and were at higher risk of developing adverse drug reactions (ADRs). 2 Multiple strategies are used to reduce the number of ADRs among children with complex conditions, and pharmacogenomics-guided drug therapy has emerged as one of the options.
][10][11] Despite the increasing number of pharmacogenomics implementation projects, the integration of PGx testing into real-time clinical care and decisionmaking has been challenging.These challenges have mainly been associated with implementation barriers, such as the paucity of regulated clinical PGx testing, limited literacy and comfort with regard to PGx testing among health care professionals, and the lack of integration of PGx data into the electronic health record. 12,13o modes of PGx testing are available to identify the need for clinical evaluation regarding past, current, or upcoming drug therapy. 14The point-of-care model, also known as the reactive model, addresses only 1 or more targeted gene-drug combinations and is typically guided by clinical evaluation at the time of prescription or in response to an emerging or past ADR, including lack of therapeutic benefit.The preemptive PGx model is an active approach that addresses potential drug therapies by using genotyping strategies that involve the testing of multiple pharmacogenes regardless of an individual's medication history.Although the use of a multiplex genotyping platform is standard when implementing the preemptive PGx approach, data from deep sequencing that were obtained for other purposes can also be used to extract PGx information. 11,15Given the diagnostic utility of whole-genome sequencing (WGS) in pediatric medicine, the preemptive WGS-guided PGx approach appears to be a reasonable option, particularly in tertiary care settings.This study assessed the implementation and clinical utility of a PGx testing program that used both a point-of-care targeted drug approach and a preemptive WGS-guided approach within a pediatric tertiary hospital.

Setting
This pilot cohort study was conducted in collaboration with the Division of Clinical Pharmacology and Toxicology at The Hospital for Sick Children, University of Toronto, and the Cardiac Genome Clinic at the Ted Rogers Centre for Heart Research. 16A pharmacogenomics clinic with a consultation program was established to advise health care professionals about pharmacogenomics-based therapeutic recommendations using annotated PGx guidelines.The study was approved by the research ethics board of The Hospital for Sick Children, and written informed consent was obtained on behalf of all

Participants
The study included 2 independent patient cohorts (point-of-care and preemptive) who were recruited through The Hospital for Sick Children.

Point-of-Care Cohort
The point-of-care cohort represented the targeted drug-guided approach and comprised 57 eligible patients (both outpatient and inpatient) who were enrolled by the clinical pharmacological consultation service between March 2017 and September 2020.By study design, patients were eligible for inclusion if they were designated to receive a drug and/or had developed an ADR or experienced lack of therapeutic benefit after receiving a drug (Table 1) that was annotated using PGx information detailed on the PharmGKB website 17  who experienced unexpected drug responses and/or with requests for guidance on drug therapy.
Patients receiving cancer and cancer-associated care were excluded from the study.

Preemptive Cohort
The preemptive cohort represented the WGS-guided PGx approach and comprised 115 children with cardiac disease who were recruited through the cardiac genome clinic between January 2017 and December 2019.

Genotyping
For the point-of-care cohort, DNA was extracted using a buccal swab; for the preemptive cohort, banked DNA from whole blood was used to confirm the presence of PGx variants of interest.

Reporting
For each patient, 6 pharmacogenes were tested: CYP2D6, CYP2C9, CYP2C19, CYP3A5, TPMT, and VKORC1.Patients' phenotype statuses could warrant a deviation in standard dosing based on the potential for variants to alter enzyme activity, as summarized in the drugs' labeling information and established clinical practice guidelines (Table 1). 17All patients received a report that included genotyping results and phenotype interpretation (ie, metabolism status).Patients received counseling from a pharmacist and/or clinical pharmacologist regarding the implications of their PGx testing results.The patient's health care team (Table 2) was informed to help guide clinical medication dosing, and the PGx report and consultation note were documented in the electronic health record of each patient.

Statistical Analysis
To summarize PGx test outcomes, each patient was categorized based on the presence of pharmacogenomics-based recommendations that warranted deviation from standard therapeutic regimens.Descriptive statistics were used to summarize cohort characteristics.

Results
A

Point-of-Care Approach
In the point-of-care cohort, 24 of 57 children (42.1%) had initiated therapy with 1 or more medications listed in the pharmacogenomics guidelines before the consultation; 18 children (31.6%) received testing to inform upcoming therapy with one of the PGx targeted drugs, and 15 children (26.3%)

Case Summaries Warfarin
Pharmacogenomic test results indicated increased sensitivity to warfarin [18][19][20] among 4 children who were actively receiving warfarin therapy.In 3 of these 4 patients, clinicians had difficulty determining the optimal therapeutic dose at initiation of warfarin therapy.In 1 instance, the international normalized ratio was found to be at supratherapeutic levels (ie, >5) after the initial standard dose of warfarin was administered, which put the child at an increased risk of bleeding.

Proton Pump Inhibitors
Five children who were already receiving proton pump inhibitors, such as pantoprazole, omeprazole, or lansoprazole, and experiencing little or no symptom relief were found to have rapid CYP2C19 metabolism.This genotype has been associated with lower exposure to proton pump inhibitors, resulting in a lack of therapeutic benefit among patients receiving standard dosing.Thus, if PGx test results had been available a priori, a different dosing regimen and/or a medication not sensitive to the CYP2C19 metabolizing enzyme would have been chosen. 21In another 4 patients, expected phenotypes of CYP2C19 helped to further guide proton pump inhibitor dosing for long-term receipt because PGx results suggested that these patients had intermediate or low CYP2C19 metabolism. 22,23

Clopidogrel
Five children receiving clopidogrel, an antiplatelet medication, received genotyping and were found to have intermediate or low CYP2C19 metabolism and a loss-of-function CYP2C19 allele.Since clopidogrel therapy requires activation, mainly via CYP2C19, these children had an increased risk of experiencing a lack of therapeutic benefit. 24,25Three of the 5 children were precardiac transplant patients who experienced a lack of therapeutic benefit (thrombotic events) with clopidogrel therapy.
The therapeutic regimen of all 5 patients was subsequently switched to an alternate drug (aspirin).received treatment with a standard dose of clopidogrel.[26] Tacrolimus Three heart transplantation recipients receiving tacrolimus were found to have CYP3A5 expression.
All 3 patients exhibited difficulty in achieving optimal dosing.Per Clinical Pharmacogenetics Implementation Consortium guidelines, these children would have benefited from an increased starting dose, as their increased metabolism interfered with achieving therapeutic levels of tacrolimus based on standard dosing guidelines. 27,28

Ondansetron
One patient had a duplication of CYP2D6 functioning alleles and was therefore considered to have ultrarapid CYP2D6 metabolism.This genotype is associated with increased metabolism of ondansetron, 29 and, as expected, impaired therapeutic response to ondansetron was observed.

Selective Serotonin Reuptake Inhibitors
The point-of-care group included children and adolescents who either experienced an impaired therapeutic response to antidepressant medications or received evaluations for potential psychiatric treatment with drugs included in PGx guidelines (Table 1).In 13 of these patients, expected CYP2D6 1][32][33] In 1 patient, reduced CYP2C19 metabolism was consistent with excessive weight gain from the previous receipt of escitalopram therapy. 31

Discussion
This cohort study describes the process outcomes 14 of the clinical implementation of a pharmacogenomics program in a pediatric tertiary hospital among both outpatients and inpatients.
In the point-of-care cohort, approximately 40% of test results warranted modification of standard dosing regimens.In the preemptive cohort, 80% of test results supported deviation from standard dosing regimens with potential drugs based on at least 1 of the 6 pharmacogenes (Figure).These frequencies of 40% to 80% for nonstandard dosing recommendations are consistent with the combined event rates of the respective genes involved. 8ing to its potential to estimate an individual patient's treatment response, PGx testing is becoming one of the pillars of individualized precision health care. 345][36] The current results focused on deviation from standard regimens, but PGx results warranting the use of a standard regimen are equally important in clinical pharmacotherapeutic decision-making.The term actionable phenotypes is misleading if used only to describe phenotype results warranting deviation from standard regimens because results supporting both modified and standard regimens are actionable.[42] The importance of using PGx testing to advance improvements in heart transplant clinical care and patient outcomes has been debated. 28,43To our knowledge, the present study provides the first comprehensive set of PGx data for pediatric heart transplantation.We informed clinicians about PGx variants present in 8 cardiac transplant candidates and 4 heart transplant recipients, which may have helped to prevent or explain treatment-associated adverse events and resulted in modified dosing regimens for 75% of those children.For example, 3 of the 4 heart transplant recipients experienced variability in tacrolimus drug concentrations that increased rejection risk owing to underdosing based on their CYP3A5 enzyme expression. 27,28Clopidogrel, a platelet aggregation inhibitor, is often used as an additive agent to prevent pretransplantation thrombotic events among children with left ventricular assistive devices, such as the Berlin Heart EXCOR (Berlin Heart Group). 25However, 4 children experienced a thromboembolic event while receiving clopidogrel, and 3 of those children had reduced CYP2C19 activity.Warfarin, an anticoagulant, is commonly prescribed in pediatric populations, mainly for the treatment of thromboembolic disorders, as prophylaxis for heart valve replacement, after the receipt cavopulmonary shunts, and before Fontan completion surgery among patients with complex congenital heart disease. 19,20In children, a large proportion of the variability in warfarin dose requirements may be explained by the variants in VKORC1 and CYP2C9, as observed in 3 of the children in our study who were considered warfarin-sensitive. 19,21,42Further studies are needed to assess the prospective value of genotype-guided dosing at initiation of and during warfarin therapy in the pediatric population.
Testing via WGS has become increasingly common among children with undiagnosed complex medical conditions. 44,45In this study, WGS was incorporated into the PGx analysis framework. 11p347) The present study examined the implementation outcomes and benefits of PGx testing in 2 different cohorts, and the findings indicated that clinically useful information can be derived from both reactive and prospective testing.However, as the field of pharmacogenomics continues to expand and testing becomes more widely available, we propose that PGx testing and/or analysis (in the context of genome sequencing conducted for other medical reasons) be performed in a preemptive manner as often as possible.Although reactive testing results can help to explain previous adverse effects and/or therapeutic shortcomings, they often occur in a context in which a patient is harmed to some extent.Pharmacogenomic testing conducted in a preemptive manner would likely prevent these clinical scenarios from occurring and therefore provide patient care that is safer and more efficient while curtailing substantial expenses, as reported in a recent costeffectiveness analysis of preemptive pharmacogenetic tests. 46

Limitations
This study has limitations.The comprehensive clinical utility of PGx testing warrants further analysis, given that each drug-gene combination was not explored separately in the point-of-care cohort because of sample size limitations.Therefore, it was not possible to analyze the diagnostic value of PGx tests for assessing past or ongoing ADRs or lack of therapeutic benefit specific to each gene-drug pair.Multi-institutional collaborative efforts are needed to examine these questions.
Notably, pharmacodynamic factors, including receptor and transporter variations in neurotransmitters, have been identified as important factors associated with the therapeutic benefits of antidepressant, antipsychotic, stimulant, and antiadrenergic medications. 33These pharmacodynamic factors will eventually need to be integrated into PGx testing, and their variations are currently being investigated for use as psychopharmacologic interventions among children and adults. 33Further research is warranted to increase the clinical utility of PGx testing among children and adolescents with mental health conditions.

JAMA Network Open | Pharmacy and Clinical Pharmacology
Implementation of Pharmacogenomic Testing in Pediatric Tertiary Care This clinic was established by the Ted Rogers Centre for Heart Research to investigate genetic factors associated with an individual's susceptibility to risk factors for heart failure and/or a diagnosis of heart failure.Patients in the cardiac genome clinic received exploratory WGS 16 to identify potential genetic associations with their cardiac disease.As part of the analysis, PGx data were manually extracted from WGS data regardless of the presence or absence of planned or current receipt of a targeted drug.If a non-*1 haplotype was identified in 1 of 6 pharmacogenes (cytochrome P450, subfamily 2D, polypeptide 6 [CYP2D6; OMIM 124030); cytochrome P450, subfamily 2C, polypeptide 9 [CYP2C9; OMIM 601130], cytochrome P450, subfamily 2C, polypeptide 19 [CYP2C19; OMIM 124020]; cytochrome P450, subfamily 3Am polypeptide 5 [CYP3A5; OMIM 605325]; thiopurine S-methyltransferase [TPMT; OMIM 187680]; and vitamin K epoxide reductase complex, subunit 1 [VKORC1; OMIM 608547]) or a non-*3 haplotype was identified in cytochrome P450, subfamily 3A, polypeptide 5 (CYP3A5; OMIM 605325), the patient's DNA sample was referred for further clinical validation via targeted genotyping at a laboratory with Clinical LaboratoryImprovement Amendments certification.16

Table 1 .
Drug-Gene Interactions and Pharmacogenomic Variants Identified by Targeted Genotyping Abbreviations: CNV, copy number variant; SNV, single nucleotide variant.
total of 172 children (mean [SD] age, 8.5[5.6]years;108 boys [62.8%]) were enrolled in the study.As shown in the Figure, 57 patients in the point-of-care cohort (mean [SD] age, 10.3 [5.5] years; 32 boys [56.1%]) were referred to the pharmacogenomics clinic for drug therapy guidance with regard to cardiovascular agents, proton pump inhibitors, and psychiatric medications.In the preemptive cohort, the WGS data of 115 children (mean [SD] age, 7.6 [5.4] years; 76 boys [66.1%]) were examined for PGx information within the 6 pharmacogenes.Overall, 126 participants (73.3%) were receiving care from cardiology services.

Table 2 .
Clinical Service Referrals for Pharmacogenomic Consultation a The point-of-care cohort comprised 57 patients recruited from the consultation clinic who received the targeted drug-guided approach.The preemptive cohort comprised 115 patients recruited from the cardiac genome clinic who received the whole-genome sequencing-guided approach.Figure.Patient Flowchart and Overview of Pharmacogenomic Data Integration a PGx indicates pharmacogenomic; WGS, whole-genome sequencing.aNon-*1haplotype in CYP2C9, CYP2C19, CYP2D6, and TPMT; VKORC1 1639 G>A (GA variant in the presence of CYP2C9*1/*1 is defined as a reference); and non-*3 haplotype in CYP3A5.JAMA Network Open | Pharmacy and Clinical PharmacologyImplementation of Pharmacogenomic Testing in Pediatric Tertiary Care JAMA Network Open.2021;4(5):e2110446.doi:10.1001/jamanetworkopen.2021.10446(Reprinted) May 26, 2021 5/12 Downloaded From: https://jamanetwork.com/ on 09/16/2023 Preemptive Approach In the preemptive cohort, 14 of 115 children (12.2%) exhibited the reference genotypes in all 6 pharmacogenes (Figure).Samples of DNA from the remaining 101 children (87.8%) were further tested using the multiplex PGx genotyping panel.The combined PGx results of the preemptive cohort indicated that a modified drug selection and/or dosing regimen for at least 1 drug-gene combination was recommended for 92 children (80.0%), while standard regimens were compatible with all tested genes in the remaining 23 children (20.0%) (eTable in the Supplement).

Table 2 )
, which explains the common receipt of medications such as clopidogrel, tacrolimus, and warfarin in the patient cohorts.Although limited by our patient selection, the results of this pilot study are consistent with those of previous studies performed among adult and pediatric populations, which