Recurrent venous thrombosis during direct oral anticoagulant therapy in a patient with protein S deficiency

Protein S (PS) deficiency is an inherited thrombophilia associated with an increased risk of venous thromboembolism (VTE). In Japan, unfractionated heparin followed by warfarin has been historically applied for the treatment of VTE. Recent evidence showed that direct oral anticoagulants (DOACs) were non-inferior to standard therapy with warfarin, with significantly less bleeding in patients with VTE. However, it is unknown whether DOACs are effective for the treatment of VTE in patients with thrombophilia, including protein S deficiency, due to lack of evidence. Here, we report a case of recurrent venous thrombosis during edoxaban therapy in a patient with protein S deficiency, which was successfully treated using high-dose apixaban therapy.