Objectives: Rheumatology medications are often associated with adverse drug reactions (ADRs) or inadequate response (IR). Pharmacogenomics may be a solution, but there is limited knowledge of its potential utility within rheumatology.
Methods: We analysed medication changes and pharmacogenomically actionable prescriptions for all adult rheumatology outpatient encounters at our medical centre between 10/2012-12/2018. Three sources defined pharmacogenomic actionability: FDA labels, Clinical Pharmacogenetics Implementation Consortium guidelines, and our institutionally-deliverable pharmacogenomic clinical decision support (CDS) summaries. A subset of patients (validation cohort) had previously undergone broad, preemptive pharmacogenomic testing within other clinics but results were unavailable within rheumatology. We assessed the occurrence of specific pharmacogenomic ADRs/IRs in this group.
Results: From 174,834 prescribing events, 6300/7761 patients (81%) had clinically actionable pharmacogenomic drug prescriptions (i.e. institutional CDS summaries would have been deployable if testing had been done). Using more conservative standards (pharmacogenomically actionable by ≥2 guidance bodies), 4158/7761 (54%) patient prescriptions could have been impacted. The greatest proportions of potentially impacted rheumatologic prescriptions were for tramadol (47%), allopurinol (21%), azathioprine (17%) and celecoxib (8%). Among our validation cohort (94 previously-genotyped patients), 29 (31%) patients had a pharmacogenomic genotype that would have cautioned possible ADRs/IRs for ≥1 medication. Four patients actually suffered ADRs/IRs that would have been predicted by preemptive genotyping.
Conclusions: Pharmacogenomic genotyping could inform prescribing for the majority of rheumatology patients and may prevent a subset of ADRs/IRs. These findings justify prospective evaluation of pharmacogenomic testing including assessment of cost-effectiveness in selected rheumatology populations to further understand impact on therapy-related toxicities and treatment outcomes.