Abstract
Avoidance of apixaban with carbamazepine (CBZ) is recommended owing to an anticipated reduction in apixaban concentration, although this drug interaction is poorly described. We report a case wherein apixaban concentration was measured before and 2 weeks after CBZ. Apixaban concentrations were substantially reduced; hence, the dose of apixaban was doubled alongside a small increase in CBZ. Subsequent apixaban concentrations were essentially unchanged. This extent of reduction in apixaban concentration appears to be related to the dose of CBZ, with the interaction occurring over 2-4 weeks. This combination should be avoided unless apixaban concentrations can be assessed using a calibrated assay.