Appropriateness of direct oral anticoagulant dosing and its relation to drug levels in atrial fibrillation patients

Direct oral anticoagulants (DOACs) are commonly administered at a level that is lower than that recommended by dose reduction criteria. This raises concern regarding the adequacy of anticoagulation achieved. To evaluate the relationship between inappropriate dosing and DOAC levels. Medical records of atrial fibrillation patients who underwent DOAC level testing during 2013–2017 were reviewed. The primary outcomes were drug levels under and above the expected steady-state range, and in the lowest and highest quartiles. Of 143 patients who underwent DOAC measurements, only 87 (60.8%) received the appropriate dose. Levels under the expected range and in the lowest quartile were found in 11.9% and 15.0% of patients treated with appropriate dosing compared to 21% and 41.5% of patients treated with inappropriately low dose. DOAC levels were above the expected range and in the highest quartile in 23.8% and 32.5% of patients treated with the appropriate dose compared to 7.1% and 9.4% treated with inappropriately low dose. In multivariate analysis, the administration of an appropriate DOAC dose was associated with a lower rate of DOAC in the lowest level (adjusted odds ratio [95% CI] 0.30 (0.12, 0.76), P = 0.011). On the other hand, appropriate dose was associated with drug levels in the highest quartile (odds ratio [95% CI] 3.77 (0.12, 0.76), P = 0.011). Treatment with inappropriately low DOAC dosing compared to appropriate dose is associated with lower DOAC levels. However, among those treated with appropriate dosing, a higher proportion had high DOAC levels above the expected range.