Coagulation assays in a case of apixaban overdose
Intentional overdose of apixaban is rare and minimal data exist regarding the usefulness of routinely available laboratory tests to predict drug levels. A 50-year-old man was admitted after ingestion of 200-mg apixaban. Serial blood samples were obtained over a 54-h period for assessment of the fall-off in drug levels using the prothrombin time/international normalized ratio and anti-Xa assays and compared with an apixaban-specific chromogenic assay. The prothrombin time/international normalized ratio and anti-Xa assays correlated with the apixaban level when the drug was in the supratherapeutic range (>130 ng/ml) but not in the typical therapeutic trough to peak levels. Apixaban levels are best assessed by a specific anti-Xa test using optimized chromogenic substrates and specific calibrators. A standard anti-Xa test can be a useful surrogate when drug levels are high but use of a specific threshold level for discharge purposes requires caution.