Unexpected acute pulmonary embolism in an old COVID-19 patient with warfarin overdose: a case report

Background Severe acute respiratory syndrome coronavirus 2 disease is strongly associated with a high incidence of thrombotic events. Anticoagulation could be a cornerstone in successfully managing severe forms of coronavirus disease 2019 (COVID-19). However, optimal anticoagulant dosing in elderly patients is challenging because of high risk of both thrombosis and bleeding. Case summary We present here the case of an 89-year-old patient receiving warfarin for atrial fibrillation and valvular heart disease, admitted to the intensive care unit for respiratory failure due to COVID-19. The patient presented with a severe epistaxis associated with warfarin overdose [international normalized ratio (INR) > 10]. After a successful initial reversal using vitamin K per os, INR values greatly fluctuated up to 10, requiring repeated administrations of vitamin K. Despite starting low-molecular-weight heparin therapy at therapeutic dose as soon as INR value was below 2.0, the patient further developed an acute bilateral and proximal pulmonary embolism concomitantly with a sharp D-dimer increase. The combination of azithromycin intake, a known inhibitor of CYP2C9, with the presence of CYP2C9*2 and -1639G>A VKORC1, two variants associated with warfarin hypersensitivity, have likely contributed to explain the warfarin overdose and the difficulty to reverse warfarin effect in this patient. Discussion This case report illustrates the complexity of COVID-19 pathophysiology and its management for physicians, especially in patients receiving vitamin K antagonists (VKAs). Infection, concurrent medication use, and pharmacogenetic factors involved in VKA metabolism and pharmacodynamics may lead to a loss of control of anticoagulation. Pulmonary embolism should still be considered in COVID-19 patients even with effective or overdosed anticoagulant therapy.