* evidence of critical covid-19 based on: * 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) * septic shock (defined by systolic blood pressure \[bp\] \< 90 mm hg, or diastolic bp \< 60 mm hg) * multiple organ dysfunction/failure * in the opinion of the investigator, unlikely to survive for at least 48 hours from screening or anticipate mechanical ventilation within 48 hours. * inadequate hematologic parameters as indicated by the following labs: * participants with severe neutropenia (anc \<1000 x 10\^9/l) or * thrombocytopenia (e.g., platelets \<100,000 per microliter of blood) * inadequate renal and liver function as indicated by the following labs: * creatinine clearance (crcl) \<20 ml/min using the formula of cockcroft and gault * aspartate transaminase (ast) or alanine transaminase (alt) \> 5 x uln * hyponatremia defined as sodium \< 135 milliequivalents per liter (meq/l). * unable to take oral medication when informed consent is obtained. * participants with a legal guardian or who are incarcerated. * treatment with strong cyp3a inhibitors or inducers. * pregnant and breastfeeding women.

* evidence of critical covid-19 based on: * 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) * septic shock (defined by systolic blood pressure \[bp\] \< 90 mm hg, or diastolic bp \< 60 mm hg) * multiple organ dysfunction/failure * in the opinion of the investigator, unlikely to survive for at least 48 hours from screening or anticipate mechanical ventilation within 48 hours. * inadequate hematologic parameters as indicated by the following labs: * participants with severe neutropenia (anc \<1000 x 10\^9/l) or * thrombocytopenia (e.g., platelets \<100,000 per microliter of blood) * inadequate renal and liver function as indicated by the following labs: * creatinine clearance (crcl) \<20 ml/min using the formula of cockcroft and gault * aspartate transaminase (ast) or alanine transaminase (alt) \> 5 x uln * hyponatremia defined as sodium \< 135 milliequivalents per liter (meq/l). * unable to take oral medication when informed consent is obtained. * participants with a legal guardian or who are incarcerated. * treatment with strong cyp3a inhibitors or inducers. * pregnant and breastfeeding women.

- evidence of critical covid-19 based on: - 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) - septic shock (defined by systolic blood pressure [bp] < 90 mm hg, or diastolic bp < 60 mm hg) - multiple organ dysfunction/failure - in the opinion of the investigator, unlikely to survive for at least 48 hours from screening or anticipate mechanical ventilation within 48 hours. - inadequate hematologic parameters as indicated by the following labs: - participants with severe neutropenia (anc <1000 x 10^9/l) or - thrombocytopenia (e.g., platelets <100,000 per microliter of blood) - inadequate renal and liver function as indicated by the following labs: - creatinine clearance (crcl) <20 ml/min using the formula of cockcroft and gault - aspartate transaminase (ast) or alanine transaminase (alt) > 5 x uln - hyponatremia defined as sodium < 135 milliequivalents per liter (meq/l). - unable to take oral medication when informed consent is obtained. - participants with a legal guardian or who are incarcerated. - treatment with strong cyp3a inhibitors or inducers. - pregnant and breastfeeding women.

- evidence of critical covid-19 based on: - 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) - septic shock (defined by systolic blood pressure [bp] < 90 mm hg, or diastolic bp < 60 mm hg) - multiple organ dysfunction/failure - in the opinion of the investigator, unlikely to survive for at least 48 hours from screening or anticipate mechanical ventilation within 48 hours. - inadequate hematologic parameters as indicated by the following labs: - participants with severe neutropenia (anc <1000 x 10^9/l) or - thrombocytopenia (e.g., platelets <100,000 per microliter of blood) - inadequate renal and liver function as indicated by the following labs: - creatinine clearance (crcl) <20 ml/min using the formula of cockcroft and gault - aspartate transaminase (ast) or alanine transaminase (alt) > 5 x uln - hyponatremia defined as sodium < 135 milliequivalents per liter (meq/l). - unable to take oral medication when informed consent is obtained. - participants with a legal guardian or who are incarcerated. - treatment with strong cyp3a inhibitors or inducers. - pregnant and breastfeeding women.

- evidence of critical covid-19 based on: - 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) - septic shock (defined by systolic blood pressure [bp] < 90 mm hg, or diastolic bp < 60 mm hg) - multiple organ dysfunction/failure - in the opinion of the investigator, unlikely to survive for at least 48 hours from screening or anticipate mechanical ventilation within 48 hours. - inadequate hematologic parameters as indicated by the following labs: - participants with severe neutropenia (anc <1000 x 10^9/l) or - thrombocytopenia (e.g., platelets <100,000 per microliter of blood) - inadequate renal and liver function as indicated by the following labs: - creatinine clearance (crcl) <20 ml/min using the formula of cockcroft and gault - aspartate transaminase (ast) or alanine transaminase (alt) > 2.5 x upper limit of normal (uln) - total bilirubin >1.5 x upper limit of normal (uln) - hyponatremia defined as sodium < 135 milliequivalents per litre (meq/l). - unable to take oral medication when informed consent is obtained. - treatment with strong cyp3a inhibitors or inducers. - pregnant and breastfeeding women.

- evidence of critical covid-19 based on: - 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) - septic shock (defined by systolic blood pressure [bp] < 90 mm hg, or diastolic bp < 60 mm hg) - multiple organ dysfunction/failure - in the opinion of the investigator, unlikely to survive for at least 48 hours from screening or anticipate mechanical ventilation within 48 hours. - inadequate hematologic parameters as indicated by the following labs: - participants with severe neutropenia (anc <1000 x 10^9/l) or - thrombocytopenia (e.g., platelets <100,000 per microliter of blood) - inadequate renal and liver function as indicated by the following labs: - creatinine clearance (crcl) <20 ml/min using the formula of cockcroft and gault - aspartate transaminase (ast) or alanine transaminase (alt) > 2.5 x upper limit of normal (uln) - total bilirubin >1.5 x upper limit of normal (uln) - hyponatremia defined as sodium < 135 milliequivalents per litre (meq/l). - unable to take oral medication when informed consent is obtained. - treatment with strong cyp3a inhibitors or inducers. - pregnant and breastfeeding women.