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

Approximately 36 participants will be enrolled sequentially into 3 cohorts. Within each cohort of 12 participants, 9 will be randomized to PLN-74809 and 3 will be randomized to placebo (3:1 ratio). * In Part 1, approximately 12 participants will be randomized to Dose level 1 of PLN-74809 or placebo QD * In Part 2, approximately 12 participants will be randomized to Dose level 2 of PLN-74809 or placebo QD * In Part 3, approximately 12 participants will be randomized to Dose level 3 of PLN-74809 or placebo QD