This is an open label randomized controlled clinical trial which was designed to confirm the potential efficacy and safety of favipiravir in the management of patients with mild to moderate COVID-19 compared to best supportive care.

Favipiravir is an antiviral agent whose indication in Japan is currently for influenza infections. There were earlier reports from China suggesting its promising potential for benefit in the treatment of COVID-19. This is an open label randomized controlled clinical trial was designed to verify the potential efficacy and safety of favipiravir in the management of patients with mild to moderate COVID-19 compared to best supportive care. This study will look at the potential of using this repurposed oral agent in managing non-severe cases of COVID19. Consenting patients admitted to hospitals or isolation/quarantine facilities will be randomized at a 2:1 ratio to either favipiravir versus best supportive care. Patients will be examined daily and will have xray and nasopharyngeal swabs every 3-4 days for close monitoring.

Inclusion Criteria:

• Age: 18 to 74 years (at the time of informed consent)
• Gender: Male or female
• Patients with SARS-CoV-2-positive nasopharyngeal swab by RT-PCR test with non-severe presentation upon admission to clinical trial site hospitals or trial-supervised quarantine facilities or under trial -supervised home isolation;
• For premenopausal female patients, patients who have been confirmed to be negative on a pregnancy test before administration of the study drug;
• Patients who understand the contents of this study and can provide written consent by themselves without assistance, or as appropriate with their assent and consent of their parents

Exclusion Criteria:

• Patient has manifestation that meets case definition of Severe COVID-19: Adult with clinical signs of pneumonia (fever, cough, dyspnea, fast breathing) plus one of the following: respiratory rate > 30 breaths/min; severe respiratory distress; or SpO2 < 90% on room air.
• Fever (37.5°C) more than 7 days after the onset of fever
• Patients with suspected concomitant bacterial infections (e.g. 1 ng/ml or higher procalcitonin, etc.) prior to initiation of study drug
• Patients with suspected concomitant fungal infections (e.g. 30 pg/ml or higher (1-3)-β-d-glucan, etc.) prior to initiation of study drug
• Patients with suspected concurrent congestive heart failure (e.g. 100 pg/mL or higher NT-pro BNP levels, etc.) prior to initiation of study drug
• Patients with severe hepatic impairment (>Grade 3: ALT >10 times of upper normal limit)
• Patients with renal impairment requiring dialysis
• Patients with disturbed consciousness such as disturbed orientation
• Pregnant or possibly pregnant patients
• Female patients who are unable to consent to contraceptive use of oral contraceptives, mechanical contraceptives such as intrauterine devices or barrier devices (pessaries, condoms), or a combination of these devices during the 7 days after the start of favipiravir administration.
• Male patients whose partner cannot agree to use the contraception method described in (10) above
• Patients who cannot consent to the use of condoms from the start of favipiravir administration to 7 days after the end of favipiravir administration
• Patients with hereditary xanthinuria
• Patients who have previously ever been diagnosed with hypouricemia (< 1 mg/dL) or xanthine urinary calculi
• Patients with a history of gout or on treatment for gout or hyperuricemia
• Patients receiving immunosuppressants
• Patients who received interferon-alpha or drugs with reported antiviral activity against SARS-CoV-2 (hydroxychloroquine sulfate, chloroquine phosphate, lopinavir-ritonavir combination, ciclesonide, nafamostat mesylate, camostat mesylate) within 9 days after fever (37.5°C or more).
• Patients in whom this episode of infection is a recurrence or reinfection of SARS-CoV-2 infection
• Patients who have previously received favipiravir (T-705a)
• Other patients judged ineligible by the principal investigator or sub-investigator