Concannon, Kennedy

ABSTRACTItraconazole and posaconazole are frequently prescribed following transplantation to prevent and treat fungal infections. Navigating drug interactions is challenging due to these agents’ potent CYP3A4 inhibition, and literature describing concurrent apixaban, a CYP3A4 substrate, is limited. This retrospective study of cardiothoracic transplant recipients evaluates the impact of itraconazole and posaconazole on apixaban exposure and reports clinical outcomes from routine apixaban dose reduction. Institutional practice reduces apixaban to 2.5 mg twice daily with itraconazole or posaconazole and obtains apixaban therapeutic drug monitoring (TDM), expected range 34–230 ng/mL. Eighteen levels collected in 15 patients on itraconazole displayed a median [IQR] apixaban trough of 143 ng/mL [95–195]. Fifteen levels collected in 13 patients on posaconazole displayed a median [IQR] apixaban trough of 124 ng/mL [93–174]. Two major bleed events, three VTE, two stroke, and eight instances of clot resolution were identified. Reduced‐dose apixaban resulted in apixaban exposure similar to normal dosing in the general population. Apixaban TDM is encouraged for individualized dosing when administered with itraconazole and posaconazole.