Trends and implementation of preemptive pharmacogenomic testing

Preemptive pharmacogenomic testing represents an aspirational practice in precision medicine to enable uniform and widespread use of genotyping to predict drug-gene interactions across and throughout the patient journey to optimize therapeutic efficacy and minimize adverse drug reactions. The frequency of drug-gene interactions is high, with nearly all patients expressing at least one known clinically actionable pharmacogene and being treated within a 5-year period with a drug that might interact with a clinically relevant pharmacogenetic variant. Some use cases for pharmacogenomics involving drug-genotype-disease triads, such as vitamin K inhibitors are well studied and unambiguously cost effective and beneficial to patients. As such these have been readily converted to consensus clinical practice. Other use cases, such as the use of genotyping the gene encoding dihydropyrimidine-dehydrogenase to guide fluoropyrimidine use, involve controversy due to a low frequency of life-saving benefits. As such, the prediction of phenotypes from genotypes continues to be challenging, in part because the knowledge base is dynamic. While pharmacogenomics is a highly collaborative community of practice, health informatics silos impede the fluid movement of genotyping information across providers and other domains within the healthcare ecosystem. Regional and organizational differences in medical practice, clinical workflows, and knowledge about pharmacogenomics practice also present barriers to broad implementation. Leading institutions have freely shared what they have learned from their preemptive testing efforts, but not all lessons are generalizable. Ethical and reimbursement issues are complex and render consensus guidelines and best practices vulnerable, and occasionally conflictive. Complexities such as polyvariant pharmacophenotypes, polypharmacy, and phenoconversion limit the application of a reductionist approach that creates guidelines predicated on simple drug-genotype-disease triads. Variability in genotyping assay content, variant interpretation, and clinical decision support systems are opportunities that can be explored to expedite implementation of preemptive pharmacogenomics practice.