Inclusion Criteria:

• - Patient aged ≥ 50 years.

• - Patient with Idiopathic Pulmonary Fibrosis satisfying the ATS/ERS/JRS/ALAT diagnostic criteria (29) diagnosed.

In the absence of a surgical lung biopsy, high-resolution computed tomography (HRCT) must be "consistent with Usual Interstitial Pneumonia (UIP)" defined as meeting either criteria A, B, and C, or criteria A and C, or criteria B and C below: A. Definite honeycomb lung destruction with basal and peripheral predominance. B. Presence of reticular abnormality and traction bronchiectasis consistent with fibrosis, with basal and peripheral predominance. C. Atypical features are absent, specifically nodules and consolidation. Ground glass opacity, if present, is less extensive than reticular opacity pattern.

• - - Patient who fulfill at least 1 of the 4 criteria for IPF progression in the 12 months (+/- one six months) before screening, despite antifibrotic treatment in clinical practice (if yes check the option(s)).

These criteria are: 0 Relative decline in FVC ≥10% predicted 0 Relative decline in FVC ≥5-<10% predicted and worsened respiratory symptoms 0 Relative decline in FVC ≥5-<10% predicted and increased extent of fibrotic changes on chest imaging 0 Worsened respiratory symptoms and increased extent of fibrotic changes on chest imaging.

• - Patient must have been on a stable dose of pirfenidone or nintedanib prescribed as first-line therapy for at least 6 months, with good tolerance of 1602 to 2403 mg per day of pirfenidone or 200 to 300 mg per day of nintedanib.

• - Patient who has a FVC ≥ 45% of predicted.

• - Patient who has a forced expiratory volume in 1 second (FEV1)/FVC ratio > 0.70.

• - Patient who has a life expectancy of at least 9 months.

• - Patient who has provided his written informed consent to participate in the study.

• - Patient affiliated to a social insurance regimen.

Exclusion Criteria:

• - Patients under judicial protection.

• - Female patient who is pregnant or lactating, or is of child bearing potential (defined as a sexually mature woman not surgically sterilized or not post-menopausal for at least 24 consecutive months if ≤ 55 years or 12 months if > 55 years) and who did not agree to use highly effective methods of birth control throughout the study.

• - Patient who is currently on both pirfenidone and nintedanib.

• - Patient who has already received pirfenidone and nintedanib either concomitantly or successively.

• - Patient who has a contra-indication to pirfenidone or nintedanib.

• - Patient who has emphysema > 15% on HRCT or the extent of emphysema is greater than the extent of fibrosis according to reported results from the most recent HRCT.

• - Patient who had acute exacerbation of idiopathic pulmonary fibrosis within the previous 3 months.

• - Patient who has a history of cigarette smoking within the previous 3 months.

• - Patient who has received experimental therapy for IPF within 4 weeks before baseline.

• - Patient who is receiving systemic corticosteroids equivalent to prednisone > 15 mg/day or equivalent within 2 weeks before baseline.

• - Patient who received Immuno-suppressants (e.g. methotrexate, azathioprine, cyclophosphamide, cyclosporine, sirolimus, everolimus or other immunosuppressants) within 4 weeks before baseline.

• - Patient who has a history of a malignancy within the previous 5 years, with the exception of basal cell skin neoplasms.

In addition, a malignant diagnosis or condition first occurring prior to 5 years must be considered cured, inactive, and not under current treatment.

• - Patient who, in the Investigator's opinion, is not able to perform home spirometry in accordance with the protocol.

• - Patient who has any concurrent condition other than IPF that, in the Investigator's opinion, is unstable and/or would impact the likelihood of survival for the study duration or the subject's ability to complete the study as designed, or may influence any of the safety or efficacy assessments included in the study.

• - Patient who has baseline resting oxygen saturation of < 88% on room air or supplemental oxygen.

• - Patient who had lung transplantation or who is on a lung transplant list and the investigator anticipates the patient will not be able to complete the study prior to transplant.

Arms

Experimental: Combined therapy

Active Comparator: Switch monotherapy

Other: Control group

Interventions

Drug: - pirfenidone and nintedanib

The experimental group will receive pirfenidone 2403 mg per day (at least 1602 mg) in combination with nintedanib 300 mg per day (at least 200 mg) during 24 weeks.

Drug: - pirfenidone or nintedanib

The second intervention group will switch from one monotherapy during 24 weeks: with pirfenidone 2403 mg per day (at least 1602 mg) or nintedanib 300 mg per day (at least 200 mg) to the other monotherapy (nintedanib in patients who received pirfenidone as first line therapy before inclusion and conversely).

Drug: - pirfenidone or nintedanib

The control group will keep on the same monotherapy during 24 weeks: with pirfenidone 2403 mg per day (at least 1602 mg) or nintedanib 300 mg per day (at least 200 mg) to the other monotherapy (nintedanib in patients who received pirfenidone as first line therapy before inclusion and conversely).