Tolerability of favipiravir therapy in critically ill patients with COVID‐19: A report of four cases.

Favipiravir (FVP) is an RNA polymerase inhibitor with broad antiviral activity.1 FVP is a prodrug that is ribosylated and phosphorylated intracellularly to form the active metabolite and has a short half-life (2-5.5 h) after oral administration.2 It is registered for the treatment of influenza infection in Japan and has been used in clinical trial for the treatment of Ebola virus infection (EBOV). All patients had increasing lymphocytes count during the course of FVP therapy, except the patient who deceased. FVP concentrations were found much lower than that of healthy subjects.9 Three of the four patients reported here received FVP late after symptoms onset (7-18 days), probably decreasing the possibility of an antiviral effect. [Extracted from the article]