A Favipiravir-induced Fever in a Patient with COVID-19.

We herein report the first case of a fever induced by favipiravir, a potential coronavirus disease 2019 therapeutic drug. An 82-year-old man diagnosed with bilateral pneumonia was transferred to our hospital following a positive severe acute respiratory syndrome coronavirus 2 polymerase chain reaction test. He was treated with compassionate use of favipiravir. Both his oxygen demand and fever gradually improved after admission; however, his fever relapsed, and the C-reactive protein (CRP) levels increased on day 7. We diagnosed his fever as being favipiravir-induced. The fever resolved a few days after favipiravir discontinuation, demonstrating the accuracy of the diagnosis. This case revealed that favipiravir can induce a fever.