Scalable System-Wide CYP2C19 Pharmacogenomic Testing Reveals 38% Excess Incidence of Adverse Events in Metabolizers Receiving Inappropriate Prescriptions

Abstract Objective In spite of evidence and recommendations reflecting the importance of pharmacogenomic testing, most prescriptions are still given without testing. We demonstrate the real world implications of the use of testing and evaluate adverse events and outcomes in individuals who did not receive pharmacogenomic testing for clopidogrel. Methods We analyzed ~100K individuals with paired EHR and exome sequencing data from population health studies administered at multiple medical centers using the Helix Exome+ ® assay. We inferred clopidogrel dosage by processing the prescription with an LLM. We identified all instances of individuals with at least one prescription that is not in concordance with their CYP2C19 genotype. Lastly, we identify instances of thrombosis using a comprehensive codeset based on ICD9, ICD10, and SNOMED terms. Results We identified 16,140 prescriptions of clopidogrel given to 3,853 participants. We found that 29% of these individuals have a mismatch between the recommended clopidogrel dosage guideline based on their CYP2C19 genotype and their actual prescribed daily dosage. 25% of poor metabolizers experienced thrombosis, with 40% occurring within 2 months of treatment. Poor and intermediate metabolizers receiving clopidogrel are much more likely to experience thrombosis and myocardial infarction (binomial p- value = 0.001). Conclusions We estimate a 38% excess of adverse events occur in poor and intermediate metabolizers relative to normal and rapid metabolizers. The lack of testing may be responsible for 1 thrombosis event per every ~30 people prescribed clopidogrel.