Introduction

Adverse drug reactions (ADRs) frequently occur in patients despite appropriate drug dosage and administration.1Idiosyncratic type B ADRs account for approximately 20% ADRs and are mostly immune-mediated and unpredictable.2 Occasionally, type B reactions can have serious consequences, such as severe cutaneous adverse reactions (SCARs) including Stevens–Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and drug-induced hypersensitivity syndrome/drug reaction with eosinophilia and systemic symptoms (DRESS), resulting in death.3,4 Individual genetic variability results in susceptibility to different ADRs; therefore, it is crucial to utilize the genomic data of patients for drug prescription.3Currently, various genetic tests are performed in hospitals, and a vast amount of genetic information is already pre-stored in electronic medical records (EMRs). However, this information is rarely used for indications outside its primary purpose.
Lack of integration between the genetic information of the patient and the EMRs is an obstacle in patient-specific drug prescription at the point-of-care.4 Data on major pharmacogenomic (PGx) variants pre-stored in the EMR should be used when prescribing high-risk drugs to patients.3,5,6 The clinical validity of the drug–gene relationship used in this approach is mainly based on the Clinical Pharmacogenetics Implementation Consortium guidelines.7 Preemptive genotyping has many advantages compared to reactive genotyping. For example, the genotype information of patients can be used without delay in the prescription process. The genotype information can also be used to build a system to support physicians in making personalized prescription decisions. Furthermore, preemptive genotyping is a cost-effective approach as many drug-related variants can be obtained using a single panel.8 In reality, preemptive genotyping is not widely used in clinical practice, and PGx genes and variants found in a majority of PGx panels mainly focus on the pharmacokinetic/pharmacodynamic genes, including cytochrome P450 enzyme families.4 Therefore, these PGx genes are not tested for purposes other than their use in drug prescription.
In recent decades, particular human leukocyte antigen (HLA) alleles have been found to be strongly associated with the development of certain drug-related SCARs.9,10 We hypothesize that use of HLA PGx alleles can prevent SCARs. Despite the strong associations between some HLAs and drug-related SCARs, pre-stored HLA data obtained from transplant workup tests are not being utilized to screen individuals at a risk of developing SCARs when high-risk drugs are prescribed. Storing HLA data in a structured, standardized format in EMRs is challenging as different testing methods have been used to determine HLAs over the years. Nonetheless, if pre-existing HLA data can be successfully retrieved and re-used based on the PGx indications, it would reduce the costs of testing and effort required to obtain the same HLA information. A clinical decision support system using the pre-stored genetic data can also be utilized as a part of the point-of-care if successfully integrated.
In a previous study, we extracted, parsed, and saved the HLA data of transplant patients in a structured, standard format from pre-stored unstructured HLA data.11 This study investigated the potential clinical benefits of using the extracted HLA genotypes as a risk prediction marker for ADR.