A Study of Serial Monitoring of DOAC Levels: A Lesson of What Test to Order and When to Order it
2018
The new direct oral anticoagulants (DOACs) are an attractive choice for prevention of stroke in atrial fibrillation, prophylaxis of hip/knee replacement and treatment of venous thromboembolism (VTE).DOACs have gained popularity over warfarin as their therapeutic range can be achieved rapidly, have fewer drugdrug interactions and have fewer food restrictions.But more importantly, DOACs do not require routine monitoring.Nonetheless, there is great uncertainty and lack of consensus about how to monitor patients on DOACs that are at risk of bleeding due to renal disease, trauma, or being underweight, or on the other hand, may be subtherapeutic due to malabsorption, obesity or lack of compliance.Herein we present our experience using several methods to monitor the direct FXa inhibitors, rivaroxaban and apixaban, in a serial study of compliance.We studied the sensitivity of prothrombin time (PT), partial thromboplastin time (PTT), dilute Russell viper venom (DRVVT) and two anti-Xa chromogenic assays to measure rivaroxaban and apixaban levels in patients at serial time points for up to 12 weeks.We determined that DRVVT is a good assay to screen for the presence of DOACs but not reliable to monitor the drug levels whereas the chromogenic anti-Xa assays should be used to monitor drug level.We observed a broad range of drug levels based on the time gap from last dose and thus we recommend that blood samples be drawn at peak intervals.