[Significant Prolongation of the International Normalized Ratio Associated with COVID-19 Treatment: Possible Drug Interaction with Remdesivir].

A 55-year-old man with hypertrophic cardiomyopathy and a pacemaker was admitted with coronavirus disease 2019 (COVID-19). Before admission, the patient's medications included amiodarone, diltiazem, bisoprolol, atorvastatin, etizolam, and warfarin (WF). After admission, dexamethasone (DXM) and remdesivir (RDV) were initiated for treating COVID-19. The international normalized ratio (INR) on admission was 1.8, which increased to 3.4 on day 5 and to 6.9 on day 10 after admission. Although there have been reports that RDV may occasionally prolong prothrombin time and that the degree of prolongation is often less severe, the mechanism of action has not been elucidated till date. There are reports of prolonged INR when WF is co-administered with RDV and DXM, suggesting that drug interactions may be a potential cause for the prolongation. A similar drug interaction may have potentially occurred in the case reported here. In addition, this case used amiodarone (AMD), and it has been reported that the RDV concentration increases when used in combination with AMD. Further investigations are needed to elucidate the cause of INR prolongation. Thus, close monitoring of the patient is recommended when RDV is co-administered with high-risk agents to avoid unnecessary side effects.