1.Evidence of critical COVID-19 based on: a.Respiratory failure (defined by endotracheal intubation and mechanical ventilation, oxygen delivered by noninvasive positive pressure ventilation, or clinical diagnosis of respiratory failure in setting of resource limitations) b.Septic shock (defined by investigator assessment or requiring vasopressors) c.Multiple organ dysfunction/failure 2.In the opinion of the investigator, unlikely to survive for at least 48 hours from screening 3.Inadequate hematologic parameters as indicated by the following labs: a.Patients with severe neutropenia (ANC <1,000 x 109/L) or b.Thrombocytopenia (e.g., platelets <100,000 per microliter of blood ) 4.Inadequate renal function and liver function as indicated by the following labs: a.creatinine clearance (CrCL) <20 mL/min using the formula of Cockcroft and Gault. b.Aspartate transaminase (AST) or alanine transaminase (ALT) >5x the upper limit of normal 5.Unable to take oral medication when inform consent is obtained. 6.Patients with a legal guardian or who are incarcerated. 7.Pregnant and breastfeeding women

1.Evidence of critical COVID-19 based on: a.Respiratory failure (defined by endotracheal intubation and mechanical ventilation, oxygen delivered by noninvasive positive pressure ventilation, or clinical diagnosis of respiratory failure in setting of resource limitations) b.Septic shock (defined by investigator assessment or requiring vasopressors) c.Multiple organ dysfunction/failure 2.In the opinion of the investigator, unlikely to survive for at least 48 hours from screening 3.Inadequate hematologic parameters as indicated by the following labs: a.Patients with severe neutropenia (ANC <1,000 x 109/L) or b.Thrombocytopenia (e.g., platelets <100,000 per microliter of blood ) 4.Inadequate renal function and liver function as indicated by the following labs: a.creatinine clearance (CrCL) <20 mL/min using the formula of Cockcroft and Gault. b.Aspartate transaminase (AST) or alanine transaminase (ALT) >5x the upper limit of normal 5.Unable to take oral medication when inform consent is obtained. 6.Patients with a legal guardian or who are incarcerated. 7.Pregnant and breastfeeding women