Evaluation of the Safety, Tolerability, and Pharmacokinetics of PLN-74809 in Participants With Acute Respiratory Distress Syndrome (ARDS) Associated With at Least Severe COVID-19

Inclusion Criteria: * Diagnosis of ARDS (Berlin Criteria) * Hospitalized with at least severe COVID-19 (FDA 2020) * Receiving support for acute lung injury/respiratory distress via supplemental oxygen * Serum aspartate aminotransferase (AST) concentration ≤ 120 U/L and serum alanine aminotransferase (ALT) concentration ≤ 150 U/L * Serum total bilirubin ≤ 1.8 mg/dL, in the absence of Gilbert's syndrome or hemolysis Exclusion Criteria: * Greater than 72 hours since time of onset of ARDS. * Greater than 7 days since start of mechanical ventilation. * Currently receiving or anticipated to receive extracorporeal life support (ECLS), extracorporeal membrane oxygenation (ECMO) or high-frequency oscillatory ventilation * Unwillingness to follow lung protective ventilation strategy (i.e., tidal volume of 6 mL/kg of predicted body weight and prone positioning) and fluid management protocol (Fluids and Catheters Treatment Trial \[FACTT\] Conservative or Lite) per local institutional standards (HFOV).