This is a Phase 2, multicenter, randomized, double-blind, placebo-controlled, study to evaluate the efficacy, safety, and tolerability of 200 mg twice daily (BID) of BBT-877 in patients with IPF, with or without AF approved background therapies (pirfenidone or nintedanib).

Inclusion Criteria:

• Male patients who have completed family planning or female patient, aged 40 years or older
• Diagnosis of IPF in accordance with American Thoracic Society/European Respiratory Society/Japanese Respiratory Society/Latin American Thoracic Association guidelines for diagnosis in effect at the time of screening
• Chest high-resolution computed tomography (HRCT) performed according to ATS guidelines within 12 months prior to screening and according to minimum requirements for IPF diagnosis by central review based on HRCT and lung biopsy. If no historical acceptable HRCT is available prior to screening, an HRCT can be performed during screening. In both cases, a central reading of the HRCT has to be done as well as a review of lung biopsy slides, if available and potentially supportive for diagnosis.
• Able to walk at least 150 meters during the 6MWT at screening
• Resting oxygen saturation of ≥89% using a maximum of 6 L/min of supplemental oxygen at sea level, and up to 8 L/min at altitude during screening
• FVC ≥45% predicted of normal
• Ratio of forced expiratory volume in the first second (FEV1) to FVC ≥0.7
• Diffusing capacity for the DLCO corrected for hemoglobin ≥30% predicted of normal
• Absence of IPF improvement in the past year, as determined by the investigator
• Patients receiving either pirfenidone or nintedanib, should be on it for at least 3 months and with a stable dose in the 4 weeks prior to screening, OR taking neither pirfenidone

Exclusion Criteria:

• Unable to perform spirometry as per ATS
• Evidence of IPF exacerbation within 3 months prior to and/or during screening
• Evidence of emphysema extent greater than the extent of fibrosis
• Current smoker (tobacco, e-cigarette)
• History of lung transplant or lung volume reduction surgery
• Current immunosuppressive condition
• Estimated life expectancy of less than 12 months or 30 months in the opinion of the investigator
• Congestive heart failure class III or IV according to New-York Heart Association classification
• Pulmonary hypertension (PH) requiring PH specific therapy
• Unstable cardiovascular, pulmonary or other disease within 6 months prior to screening or during the screening period
• Use of other medications likely to interfere with study assessments
• Any other current or prior medical condition, medical or surgical therapies, or clinical trial participation expected to interfere with the conduct of the study or the evaluation of its results