Study of Efficacy and Safety of Pirfenidone in Patients With Fibrotic Hypersensitivity Pneumonitis

Inclusion Criteria: 1. Multidisciplinary consensus diagnosis of FHP, defined from the first instance in which a patient was informed of having FHP for at least 3 to 6 months. 2. Age 18 through 80 years at randomization. 3. Diagnosis of typical or compatible FHP by HRCT according to pre-specified criteria (Note: HRCT scan performed within 6 months of the start of screening may be used if it meets image acquisition guidelines): a. Typical FHP: Evidence of lung fibrosis (reticular abnormality and/or, traction bronchiectasis and/or, architectural distortion, and/or honeycombing) with either of the following: i. Profuse poorly defined centrilobular nodules of ground-glass opacity affecting all lung zones. ii. Inspiratory mosaic attenuation with the three-density sign. AND iii. Lack of features suggesting an alternative diagnosis. b. Compatible FHP: Evidence of lung fibrosis (as above) with any of the following: i. Patchy or diffuse ground-glass opacity. ii. Patchy, non-profuse centrilobular nodules of ground-glass attenuation iii. Mosaic attenuation and lobular air-trapping that do not meet the criteria for typical fibrotic HP. AND iv. Lack of features suggesting an alternative diagnosis. c. Indeterminate FHP: CT signs of fibrosis without other features suggestive of HP and lack of features suggesting an alternative diagnosis. These patients are required to have a known antigen exposure and BAL lymphocytosis (≥20%) or transbronchial biopsies demonstrating non-necrotizing granuloma(s) or lymphocytosis, or surgical lung histology consistent with HP. FHP Disease Severity and Progression 4. FVC ≥40%, DLCO ≥30% based either on historical pulmonary function tests obtained in the 30 days prior to screening or on tests obtained during screening 5. In the investigator's opinion, evidence of disease progression: worsening respiratory symptoms and an increased in the extent of fibrosis on HRCT or relative decline in the FVC% of at least 5%. 6. Able to walk ≥100 m during the 6-minute walk test (6MWT) at Screening. Informed Consent and Protocol Adherence 7. Able to understand and sign a written informed consent form. 8. Able to understand the importance of adherence to study treatment and the study protocol and willing to follow all study requirements, including the concomitant medication restrictions, throughout the study Exclusion Criteria: * Disease-Related Exclusions 1. Not a suitable candidate for enrollment or unlikely to comply with the requirements of this study, in the opinion of the investigator 2. Cigarette smoking at Screening or unwilling to avoid tobacco products throughout the study 3. Known explanation for the interstitial lung disease, including but not limited to radiation, drug toxicity, sarcoidosis, pneumoconiosis. 4. Clinical diagnosis of any connective tissue disease, including but not limited to scleroderma, polymyositis/dermatomyositis, and rheumatoid arthritis. 5. Expected to receive a lung transplant within 6 to12 months from randomization or on a lung transplant waiting list at randomization. Medical Exclusions 6. Any condition other than FHP that, in the opinion of the investigator, is likely to result in the death of the patient within 6 to12 months. 7. Any condition that, in the opinion of the investigator, might be significantly exacerbated by the known side effects associated with the administration of pirfenidone. 8. Pregnancy or lactation. Women of childbearing capacity are required to have a negative serum pregnancy test before treatment and must agree to maintain highly effective contraception by practicing abstinence or by using at least two methods of birth control from the date of consent through the end of the study. If abstinence is not practiced, one of the two methods of birth control should be an oral contraceptive (e.g., oral contraceptive and a spermicide). 9. History of ongoing alcohol or substance abuse. 10. History of severe hepatic impairment or end-stage liver disease. 11. History of end-stage renal disease requiring dialysis. 12. Clinical evidence of active infection including, but not limited to, bronchitis, pneumonia, sinusitis, or urinary tract infection. 13. Unstable or deteriorating cardiac disease, including but not limited to the following: 1. Unstable angina pectoris or myocardial infarction. 2. Congestive heart failure requiring hospitalization. 3. Uncontrolled clinically significant arrhythmias. Laboratory Exclusions 14. Any of the following liver function test criteria above specified limits: total bilirubin \> 2.0 mg/dL, excluding patients with Gilbert's syndrome; aspartate or alanine aminotransferase (AST/SGOT or ALT/SGPT) \>3 ULN; alkaline phosphatase \>2.5 ULN within past 30 days. 15. Creatinine clearance \<30 mL/min, calculated using the Cockcroft-Gault formula within the past 30 days. 16. Electrocardiogram with a QTc interval \>500 msec at Screening. Medication Exclusions 17. Prior use of pirfenidone, nintadinib or known hypersensitivity to any of the components of study treatment. 18. Introduction, increase or escalation of immunosuppressive pharmacological therapy within 1 month (e.g., prednisone, azathioprine, mycophenolic acid and mycophenolate mofetil). 19. Use of any of the following therapies within 28 days before Screening: 1. Bosentan, ambrisentan, cyclophosphamide, cyclosporine, etanercept, iloprost, infliximab, methotrexate, tacrolimus, tetrathiomolybdate, TNF-α inhibitors, imatinib mesylate, Interferon gamma-1b, and tyrosine kinase inhibitors. 2. Fluvoxamine. 3. Sildenafil (daily use). Note: intermittent use for erectile dysfunction is allowed.