Coronavirus disease 2019 was spread worldwide, as a pandemic, from December 2019. Venous thromboembolism events can inflict patients with coronavirus disease 2019 during the hospitalization or convalescent period. Therefore, monitoring of these patients, in terms of venous thromboembolism events signs and symptoms, and timely management of antithrombotic agents are of great importance.
A 45-year-old Iranian man, who is the first author of this case report, was infected by severe acute respiratory syndrome coronavirus 2 and displayed the typical signs and symptoms of coronavirus disease 2019. Although reverse transcription polymerase chain reaction for coronavirus disease 2019, and specific immunoglobulin M and immunoglobulin G against severe acute respiratory syndrome coronavirus 2, were negative at first, chest computed tomography scan showed the characteristic pattern of lung involvement of a coronavirus disease 2019 infection including bilateral and multilobar ground-glass opacities. At that time, there were no signs or symptoms of deep-vein thrombosis or pulmonary thromboembolism, so these were not investigated. About 30 hours after hospital discharge, the patient presented back to the hospital with acute-onset chest pain. We instantly tested his blood for D-dimer, and sent him to take a Doppler sonography of his lower legs and a chest computed tomography angiography in search of pulmonary thromboembolism and deep-vein thrombosis. Although we could confirm pulmonary thromboembolism with computed tomography angiography in our patient, there were no signs or symptoms of venous thromboembolism in his lower legs, and color Doppler sonography of lower limbs was normal. So, the patient was treated with rivaroxaban as an antithrombotic agent. After some days, he was discharged in good condition. About 1 month later, he was referred to our hospital because of left lower limb edema. Although he was under antithrombotic therapy, color Doppler sonography of lower limbs revealed acute deep-vein thrombosis of the left leg. Hence, we decided to shift antithrombotic therapy from rivaroxaban to warfarin, as it is more potent than rivaroxaban in recurrent venous thromboembolism and when taking new oral anticoagulants. Unlike rivaroxaban, which needs no blood test to monitor its efficacy but has a warning for signs and symptoms of bleeding, warfarin therapy must be monitored carefully by regular blood tests for prothrombin time and international normalized ratio to maintain them in the therapeutic range. The patient was informed about the bleeding cautions, and required regular check of prothrombin time and international normalized ratio to maintain them in the proper and advised range of treatment (international normalized ratio therapeutic range 2-3).
In the case of unexpected recurrent venous thromboembolism in coronavirus disease 2019, especially when patients are taking rivaroxaban or other new oral anticoagulants, such drugs should be substituted by warfarin, with routine follow-up, to maintain the value of prothrombin time and international normalized ratio within the therapeutic range.

© 2023. The Author(s).