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Background Stroke and thromboembolic events occurring among patients taking direct oral anticoagulants (DOACs) have been associated with low concentrations of DOACs. Enzyme-inducing antiseizure medications (EI-ASMs) are associated with enhanced cytochrome-P450-mediated metabolism and enhanced P-glycoprotein-mediated transport.Objective The aim of this study was to evaluate the effect of concomitant EI-ASM use on DOAC peak concentrations in patients treated in clinical care. Methods We performed a retrospective cohort study of patients treated with DOACs for atrial fibrillation and venous thromboembolic disease in an academic general hospital. In total, 307 patients treated with DOACs between August 2015 and January 2020 were reviewed. Clinical characteristics and peak DOAC plasma concentrations of patients co-treated with an EI-ASM were compared with those of patients not treated with an EI-ASM. An apixaban dose score (ADS) was defined to account for apixaban dosage and the number of apixaban dose-reduction criteria. Results In total, 177 peak DOAC plasma concentrations (including apixaban, rivaroxaban, and dabigatran) from 131 patients were measured, including 24 patients co-treated with an EI-ASM and 107 controls not treated with an EI-ASM. The proportion of patients with DOAC concentrations below the expected range was significantly higher among EI-ASM users than among patients not taking an EI-ASM (37.5 vs. 9.3%, respectively; p = 0.0004; odds ratio 5.82; 95% confidence interval [CI] 2.03-16.66). Most of these patients were treated with apixaban (85%); however, sensitivity analysis results were also significant (p = 0.031) for patients with non-apixaban DOACs. In patients co-treated with apixaban and an EI-ASM, median apixaban peak concentration was 106 ng/mL (interquartile range [IQR] 71-181) compared with 150 ng/mL in controls (p = 0.019). In multivariable analysis, EI-ASM use was associated with 6.26-fold increased odds for apixaban concentration below the expected range (95% CI 2.19-17.90; p = 0.001). Apixaban concentrations were significantly associated with EI-ASM use, moderate enzyme inhibitor use, and ADS. Conclusions Concurrent EI-ASM and DOAC use presents a possible risk for DOAC concentrations below the expected range. The clinical significance of the interaction is currently unclear. Amichai Perlman, Rachel Goldstein have contributed equally to this work.

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