1. critically ill patients, defined as those who are candidates for endotracheal intubation and mechanical ventilation, oxygen delivered by high- flow nasal cannula, (heated, humidified, oxygen delivered via reinforced nasal cannula at flow rates \>20 l/min with fraction of delivered oxygen ≥0.5), non-invasive positive pressure ventilation, extracorporeal membrane oxygenation (ecmo) , or clinical diagnosis of respiratory failure (i.e., clinical need for one of the preceding therapies, but preceding therapies not able to be administered in setting of resource limitation) and those with shock (defined by systolic blood pressure (bp) \<90 mm hg, or diastolic bp \<60 mm hg or requiring vasopressors) or multi-organ dysfunction/failure, at baseline note: the above-mentioned definition of 'critically ill' covid-19 patients is as defined in the fda guidance document "covid-19: developing drugs and biological products for treatment or prevention - guidance for industry final document" dated may 2020 2. patients in whom the first onset of symptoms/signs suggestive of covid-19 illness was observed \>10 days earlier to the baseline assessment and randomization 3. patients who have used interferon beta 1-a (ifn-β-1a) preparations or drugs with reported anti-viral action against sars-cov-2 (hydroxychloroquine sulfate, chloroquine phosphate, lopinavir-ritonavir combination drugs, ciclesonide, nafamostat mesylate, camostat mesylate) within 8 days after development of fever (≥37.5°c) note: the above-mentioned exclusion criterion is not applicable in case of patients with history of human immunodeficiency virus infection or infective hepatitis in whom use of anti-viral drugs or interferons are prescribed for treatment of the underlying condition and who are currently receiving one or more of these medications (as maintenance treatment) at the time of randomization. the infection episode in question is a relapse of, or reinfection with sars-cov-2 4. patients suspected to have a complication of congestive cardiac failure based on investigator's clinical judgement 5. patients with moderate and severe hepatic dysfunction equivalent to grade b and grade c in the child-pugh classification respectively 6. patients with alanine aminotransferase (alt) and aspartate aminotransferase (ast) levels \> 5 times upper limit of normal (uln) at screening evaluation 7. patients with renal impairment requiring dialysis 8. patients with serum uric acid higher than the uln at screening evaluation 9. patients with history of hereditary xanthinuria 10. patients who have been diagnosed with xanthine urinary calculus 11. patients with a history of gout or patients who are currently being treated for gout 12. patients who are taking immunosuppressants 13. patients who were administered favipiravir in the past 30 days 14. patients with known hypersensitivity reaction to favipiravir

1. critically ill patients, defined as those who are candidates for endotracheal intubation and mechanical ventilation, oxygen delivered by high- flow nasal cannula, (heated, humidified, oxygen delivered via reinforced nasal cannula at flow rates \>20 l/min with fraction of delivered oxygen ≥0.5), non-invasive positive pressure ventilation, extracorporeal membrane oxygenation (ecmo) , or clinical diagnosis of respiratory failure (i.e., clinical need for one of the preceding therapies, but preceding therapies not able to be administered in setting of resource limitation) and those with shock (defined by systolic blood pressure (bp) \<90 mm hg, or diastolic bp \<60 mm hg or requiring vasopressors) or multi-organ dysfunction/failure, at baseline note: the above-mentioned definition of 'critically ill' covid-19 patients is as defined in the fda guidance document "covid-19: developing drugs and biological products for treatment or prevention - guidance for industry final document" dated may 2020 2. patients in whom the first onset of symptoms/signs suggestive of covid-19 illness was observed \>10 days earlier to the baseline assessment and randomization 3. patients who have used interferon beta 1-a (ifn-β-1a) preparations or drugs with reported anti-viral action against sars-cov-2 (hydroxychloroquine sulfate, chloroquine phosphate, lopinavir-ritonavir combination drugs, ciclesonide, nafamostat mesylate, camostat mesylate) within 8 days after development of fever (≥37.5°c) note: the above-mentioned exclusion criterion is not applicable in case of patients with history of human immunodeficiency virus infection or infective hepatitis in whom use of anti-viral drugs or interferons are prescribed for treatment of the underlying condition and who are currently receiving one or more of these medications (as maintenance treatment) at the time of randomization. the infection episode in question is a relapse of, or reinfection with sars-cov-2 4. patients suspected to have a complication of congestive cardiac failure based on investigator's clinical judgement 5. patients with moderate and severe hepatic dysfunction equivalent to grade b and grade c in the child-pugh classification respectively 6. patients with alanine aminotransferase (alt) and aspartate aminotransferase (ast) levels \> 5 times upper limit of normal (uln) at screening evaluation 7. patients with renal impairment requiring dialysis 8. patients with serum uric acid higher than the uln at screening evaluation 9. patients with history of hereditary xanthinuria 10. patients who have been diagnosed with xanthine urinary calculus 11. patients with a history of gout or patients who are currently being treated for gout 12. patients who are taking immunosuppressants 13. patients who were administered favipiravir in the past 30 days 14. patients with known hypersensitivity reaction to favipiravir

critically ill patients, defined as those who are candidates for endotracheal intubation and mechanical ventilation, oxygen delivered by high- flow nasal cannula, (heated, humidified, oxygen delivered via reinforced nasal cannula at flow rates >20 l/min with fraction of delivered oxygen ≥0.5), non-invasive positive pressure ventilation, extracorporeal membrane oxygenation (ecmo) , or clinical diagnosis of respiratory failure (i.e., clinical need for one of the preceding therapies, but preceding therapies not able to be administered in setting of resource limitation) and those with shock (defined by systolic blood pressure (bp) <90 mm hg, or diastolic bp <60 mm hg or requiring vasopressors) or multi-organ dysfunction/failure, at baseline note: the above-mentioned definition of 'critically ill' covid-19 patients is as defined in the fda guidance document "covid-19: developing drugs and biological products for treatment or prevention - guidance for industry final document" dated may 2020 patients in whom the first onset of symptoms/signs suggestive of covid-19 illness was observed >10 days earlier to the baseline assessment and randomization patients who have used interferon beta 1-a (ifn-β-1a) preparations or drugs with reported anti-viral action against sars-cov-2 (hydroxychloroquine sulfate, chloroquine phosphate, lopinavir-ritonavir combination drugs, ciclesonide, nafamostat mesylate, camostat mesylate) within 8 days after development of fever (≥37.5°c) note: the above-mentioned exclusion criterion is not applicable in case of patients with history of human immunodeficiency virus infection or infective hepatitis in whom use of anti-viral drugs or interferons are prescribed for treatment of the underlying condition and who are currently receiving one or more of these medications (as maintenance treatment) at the time of randomization. the infection episode in question is a relapse of, or reinfection with sars-cov-2 patients suspected to have a complication of congestive cardiac failure based on investigator's clinical judgement patients with moderate and severe hepatic dysfunction equivalent to grade b and grade c in the child-pugh classification respectively patients with alanine aminotransferase (alt) and aspartate aminotransferase (ast) levels > 5 times upper limit of normal (uln) at screening evaluation patients with renal impairment requiring dialysis patients with serum uric acid higher than the uln at screening evaluation patients with history of hereditary xanthinuria patients who have been diagnosed with xanthine urinary calculus patients with a history of gout or patients who are currently being treated for gout patients who are taking immunosuppressants patients who were administered favipiravir in the past 30 days patients with known hypersensitivity reaction to favipiravir

critically ill patients, defined as those who are candidates for endotracheal intubation and mechanical ventilation, oxygen delivered by high- flow nasal cannula, (heated, humidified, oxygen delivered via reinforced nasal cannula at flow rates >20 l/min with fraction of delivered oxygen ≥0.5), non-invasive positive pressure ventilation, extracorporeal membrane oxygenation (ecmo) , or clinical diagnosis of respiratory failure (i.e., clinical need for one of the preceding therapies, but preceding therapies not able to be administered in setting of resource limitation) and those with shock (defined by systolic blood pressure (bp) <90 mm hg, or diastolic bp <60 mm hg or requiring vasopressors) or multi-organ dysfunction/failure, at baseline note: the above-mentioned definition of 'critically ill' covid-19 patients is as defined in the fda guidance document "covid-19: developing drugs and biological products for treatment or prevention - guidance for industry final document" dated may 2020 patients in whom the first onset of symptoms/signs suggestive of covid-19 illness was observed >10 days earlier to the baseline assessment and randomization patients who have used interferon beta 1-a (ifn-β-1a) preparations or drugs with reported anti-viral action against sars-cov-2 (hydroxychloroquine sulfate, chloroquine phosphate, lopinavir-ritonavir combination drugs, ciclesonide, nafamostat mesylate, camostat mesylate) within 8 days after development of fever (≥37.5°c) note: the above-mentioned exclusion criterion is not applicable in case of patients with history of human immunodeficiency virus infection or infective hepatitis in whom use of anti-viral drugs or interferons are prescribed for treatment of the underlying condition and who are currently receiving one or more of these medications (as maintenance treatment) at the time of randomization. the infection episode in question is a relapse of, or reinfection with sars-cov-2 patients suspected to have a complication of congestive cardiac failure based on investigator's clinical judgement patients with moderate and severe hepatic dysfunction equivalent to grade b and grade c in the child-pugh classification respectively patients with alanine aminotransferase (alt) and aspartate aminotransferase (ast) levels > 5 times upper limit of normal (uln) at screening evaluation patients with renal impairment requiring dialysis patients with serum uric acid higher than the uln at screening evaluation patients with history of hereditary xanthinuria patients who have been diagnosed with xanthine urinary calculus patients with a history of gout or patients who are currently being treated for gout patients who are taking immunosuppressants patients who were administered favipiravir in the past 30 days patients with known hypersensitivity reaction to favipiravir

1. critically ill patients, defined as those who are candidates for endotracheal intubation and mechanical ventilation, oxygen delivered by high- flow nasal cannula, (heated, humidified, oxygen delivered via reinforced nasal cannula at flow rates >20 l/min with fraction of delivered oxygen ≥0.5), non-invasive positive pressure ventilation, extracorporeal membrane oxygenation (ecmo) , or clinical diagnosis of respiratory failure (i.e., clinical need for one of the preceding therapies, but preceding therapies not able to be administered in setting of resource limitation) and those with shock (defined by systolic blood pressure (bp) <90 mm hg, or diastolic bp <60 mm hg or requiring vasopressors) or multi-organ dysfunction/failure, at baseline note: the above-mentioned definition of 'critically ill' covid-19 patients is as defined in the fda guidance document "covid-19: developing drugs and biological products for treatment or prevention - guidance for industry final document" dated may 2020 2. patients in whom the first onset of symptoms/signs suggestive of covid-19 illness was observed >10 days earlier to the baseline assessment and randomization 3. patients who have used interferon beta 1-a (ifn-β-1a) preparations or drugs with reported anti-viral action against sars-cov-2 (hydroxychloroquine sulfate, chloroquine phosphate, lopinavir-ritonavir combination drugs, ciclesonide, nafamostat mesylate, camostat mesylate) within 8 days after development of fever (≥37.5°c) note: the above-mentioned exclusion criterion is not applicable in case of patients with history of human immunodeficiency virus infection or infective hepatitis in whom use of anti-viral drugs or interferons are prescribed for treatment of the underlying condition and who are currently receiving one or more of these medications (as maintenance treatment) at the time of randomization. the infection episode in question is a relapse of, or reinfection with sars-cov-2 4. patients suspected to have a complication of congestive cardiac failure based on investigator's clinical judgement 5. patients with moderate and severe hepatic dysfunction equivalent to grade b and grade c in the child-pugh classification respectively 6. patients with alanine aminotransferase (alt) and aspartate aminotransferase (ast) levels > 5 times upper limit of normal (uln) at screening evaluation 7. patients with renal impairment requiring dialysis 8. patients with serum uric acid higher than the uln at screening evaluation 9. patients with history of hereditary xanthinuria 10. patients who have been diagnosed with xanthine urinary calculus 11. patients with a history of gout or patients who are currently being treated for gout 12. patients who are taking immunosuppressants 13. patients who were administered favipiravir in the past 30 days 14. patients with known hypersensitivity reaction to favipiravir

1. critically ill patients, defined as those who are candidates for endotracheal intubation and mechanical ventilation, oxygen delivered by high- flow nasal cannula, (heated, humidified, oxygen delivered via reinforced nasal cannula at flow rates >20 l/min with fraction of delivered oxygen ≥0.5), non-invasive positive pressure ventilation, extracorporeal membrane oxygenation (ecmo) , or clinical diagnosis of respiratory failure (i.e., clinical need for one of the preceding therapies, but preceding therapies not able to be administered in setting of resource limitation) and those with shock (defined by systolic blood pressure (bp) <90 mm hg, or diastolic bp <60 mm hg or requiring vasopressors) or multi-organ dysfunction/failure, at baseline note: the above-mentioned definition of 'critically ill' covid-19 patients is as defined in the fda guidance document "covid-19: developing drugs and biological products for treatment or prevention - guidance for industry final document" dated may 2020 2. patients in whom the first onset of symptoms/signs suggestive of covid-19 illness was observed >10 days earlier to the baseline assessment and randomization 3. patients who have used interferon beta 1-a (ifn-β-1a) preparations or drugs with reported anti-viral action against sars-cov-2 (hydroxychloroquine sulfate, chloroquine phosphate, lopinavir-ritonavir combination drugs, ciclesonide, nafamostat mesylate, camostat mesylate) within 8 days after development of fever (≥37.5°c) note: the above-mentioned exclusion criterion is not applicable in case of patients with history of human immunodeficiency virus infection or infective hepatitis in whom use of anti-viral drugs or interferons are prescribed for treatment of the underlying condition and who are currently receiving one or more of these medications (as maintenance treatment) at the time of randomization. the infection episode in question is a relapse of, or reinfection with sars-cov-2 4. patients suspected to have a complication of congestive cardiac failure based on investigator's clinical judgement 5. patients with moderate and severe hepatic dysfunction equivalent to grade b and grade c in the child-pugh classification respectively 6. patients with alanine aminotransferase (alt) and aspartate aminotransferase (ast) levels > 5 times upper limit of normal (uln) at screening evaluation 7. patients with renal impairment requiring dialysis 8. patients with serum uric acid higher than the uln at screening evaluation 9. patients with history of hereditary xanthinuria 10. patients who have been diagnosed with xanthine urinary calculus 11. patients with a history of gout or patients who are currently being treated for gout 12. patients who are taking immunosuppressants 13. patients who were administered favipiravir in the past 30 days 14. patients with known hypersensitivity reaction to favipiravir