Pirfenidone to Prevent Fibrosis in Ards.

Who May Qualify: Concomitant presence of: - ARDS (moderate and severe) - Berlin definition 1. Within 1 week of a known clinical insult or new or worsening respiratory symptoms 2. Bilateral opacities on CXR which are not fully explained by effusions, lobar/lung collapse or nodules 3. Respiratory failure not fully explained by cardiac failure or fluid overload 4. PaO2/FiO2\<200 mmHg with PEEP\<=5 cmH2O (invasive mechanical ventilation) - Inflammatory ARDS phenotype (28), defined by at least one of the following: 1. High plasma levels of inflammatory biomarkers 2. Vasopressor dependence 3. Lower serum bicarbonate or increased serum lactate - willing to sign a consent form expressed by the patient or by legal representative or on the Ethical Committee indication. - Age \>=18 years Who Should NOT Join This Trial: - Intubated and mechanically ventilated via an endotracheal or tracheostomy tube (\>7 days) up to the time of randomization - ARDS severe or moderate for more than 36 hours - Untreated pulmonary embolism, pleural effusion or pneumothorax as the primary cause of ARF - ARF fully explained by left ventricular failure or fluid overload - Consent declined - Severe chronic respiratory disease requiring domiciliary ventilation - Clinical suspicion for significant restrictive lung disease - Pregnant women or women of childbearing potential who are sexually active - Known allergy to pirfenidone - Concomitant use of fluvoxamine - Known severe hepatic failure - Known severe renal failure or necessity of dialysis not related to acute disease - Little chance of survival (SAPS II score\>75) Always talk to your doctor about whether this trial is right for you.