Fostamatinib for Treating Acute Respiratory Distress Syndrome (ARDS) in Hospitalized Adults

Inclusion Criteria: * Age ≥ 18 years old. * Subject (or legal representative) provides informed consent to study participation. * Subject (or legal representative) understands and agrees to comply with planned study procedures. * Hospitalized with acute respiratory failure from ARDS with ratio of partial pressure of arterial oxygen to fraction of inspired oxygen PaO2/FiO2 of 200 mm of Hg or less with positive end expiratory pressure (PEEP) equal to or higher than 5 cm of H2O and requiring invasive mechanical ventilation or extracorporeal support. * Functional respiratory imaging (FRI) compatible CT scan of the chest within the prior 7 days. * Duration of invasive mechanical ventilation \< 10 days. * Females of childbearing potential must agree to be abstinent or seek a highly effective form of contraception from the time of enrollment through 30 days after the last day of study drug. Exclusion Criteria: * Severe hepatic impairment (Child-Pugh Class C). * Abnormal liver function tests (AST or ALT \> 3x ULN or AST or ALT \> 3x ULN) * Pregnant or nursing. * Participation in any other clinical trial, or receipt of an investigational medicinal product within 30 days prior. * Known concomitant life-threatening disease with a life expectancy \< 6 months. * Known hypersensitivity to fostamatinib. * Uncontrolled hypertension (Systolic blood pressure \> 160 mmHg or diastolic blood pressure \> 100 mmHg). * Neutrophil count \< 1000/uL * Death expected within 72 hours * Received a live vaccine in the last 30 days * Those who were cognitively impaired or mentally disabled prior to acute illness * Patients with acute coronary syndrome, ejection fraction \<30%, or active unstable arrhythmias