This study is designed to evaluate the safety and efficacy of fostamatinib in hospitalized adult participants with acute respiratory distress syndrome (ARDS).

This is a randomized, double-blind, placebo-controlled phase 2 study for long-term evaluation of fostamatinib for the treatment of adult patients with acute respiratory distress syndrome. Subjects will be randomly assigned 1:1 to either standard of care treatment plus fostamatinib or standard or care plus placebo. Th study drug will be taken twice daily for 14 days.

The primary objective will be to evaluate drug safety in hospitalized patients with severe ARDS. Other objectives include assessment of the efficacy and clinically relevant endpoints, such as mortality and effects on resolution of this disease entity. The ability of fostamatinib to impact the short term and long term outcomes for patients with ARDS will be directly evaluated.

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