Studying the Treatment Effect of Pirfenidone in Chronic Lung Allograft Dysfunction (STOP-CLAD)

Inclusion Criteria: * Lung transplant recipients 18 years of age or older * Greater than 6 months after single or bilateral lung transplantation * Baseline FEV1 and FVC values (mean of two highest value measured 3 weeks apart) \> 50% predicted (to assure viable graft) * Diagnosis of CLAD (two consecutive spirometric values of FEV1 alone or both FEV1 and FVC \< 80% of baseline) Exclusion Criteria * Acute Rejection (AR) diagnosis by biopsy in the 28 days prior to enrollment * Treatment with pulse steroids, Anti-thymocyte Globulin (ATG), extracorporeal photopheresis (ECP), plasmapheresis, or Immunoglobulin therapy aimed at CLAD within the 28 days prior to enrollment * If the subject is receiving chronic Azithromycin therapy, the dose must be stable for the 28 days prior to enrollment * Presence of active pulmonary infection at the time of enrollment as determined by an investigator in consultation with the treating pulmonologist * Diagnosis of bronchial stenosis either a) requiring stenting, or b) thought to be responsible for the spirometric decline by principal investigator * Abnormal liver function tests (aspartate aminotransferase (AST) or alanine aminotransferase (ALT) \> 2 x upper limit of normal (ULN), Alkaline phosphatase \> 2.5 x ULN, total bilirubin \> ULN) or known cirrhosis (\>2 times upper limit of normal of AST/ALT/AP) * Total white blood cell (WBC) \< 3.0 K/uL * Moderate to Severe Renal insufficiency (CrCl \<15 mL/min calculated by the Cockcroft-Gault equation) * Use of any medication known to cause significant interactions with pirfenidone (strong CYP1A2 inhibitors such as Fluvoxamine or Enoxacin or inducers) * Pregnancy or lactation. Women of child-bearing potential will have a pregnancy test at enrollment and must agree to maintain highly effective contraception with two methods of birth control from the date of consent through the end of the study. * Tobacco use within 6 months * History of alcohol abuse in the past 1 year as determined by the treating pulmonologist * Any condition other than CLAD that will likely result in death in the next 1 year * Any condition in the judgement of the principal investigator that would preclude participation in this study * EKG with QTc interval \> 500 msec at screening * Listed for repeat lung transplantation