Nintedanib combined with or without Dextromethorphan for the treatment of IPF, with FVC as the primary efficacy endpoint to evaluate its effectivenes.

Inclusion Criteria:

1. Age ≥40 years old, regardless of gender;
2. According to "2022 ATS/ERS/JRS/ALAT Guidelines", it was diagnosed as idiopathic pulmonary fibrosis (IPF);
3. Lung function meets the following conditions during screening: forced vital capacity (FVC) ≥45% predicted value; The dispersion of carbon monoxide (DLco, corrected Hb) in a single breath is between 30% and 80% of the predicted value.
4. HRCT images completed within 12 months before screening can be used to determine UIP mode;
5. It is expected to complete the whole research plan, including 12 weeks of treatment and 1 week of follow-up;
6. Willing to follow all the requirements of drug use, visit and data collection during the study period;
7. Be able to understand the research content and sign the written informed consent;
8. Women of childbearing age provide negative pregnancy test results, and agree to take effective contraceptive measures during the study period and within 3 months after the last administration; Male subjects with fertility also need to take effective contraception at the same time.

Exclusion Criteria:

1. Suffering from other interstitial lung diseases caused by non-IPF reasons (such as connective tissue disease-related ILD, chronic allergic pneumonia, pneumoconiosis, drug-induced pneumonia, radiation lung disease, etc.);
2. One or more Acute Exacerbation)； of IPF occurred within 3 months before screening;
3. Have received a lung transplant;
4. Complicated with severe COPD(GOLD III and above), severe asthma or other airway diseases that may interfere with FVC determination;
5. The following systemic immunosuppressive treatments were used within 4 weeks before screening: > 15 mg/d prednisone (or equivalent dose), cyclophosphamide, methotrexate, tuzumab, rituximab, mycophenolate mofetil, etc.
6. Currently or in the past, allergic to Nidanib, dextromethorphan or any of its auxiliary ingredients;
7. The following laboratory abnormalities exist: ALT or AST >3×ULN；; eGFR <30 mL/min/1.73m²；
8. Have a history of uncontrolled mental illness, epilepsy, central nervous system dysfunction, or may induce adverse reactions after using dextromethorphan;
9. Being receiving drugs that may have serious drug interaction with dextromethorphan, such as monoamine oxidase inhibitor (MAOI) and selective serotonin reuptake inhibitor (SSRI), and unable to stop taking drugs;
10. Pregnant or lactating women;
11. At the time of screening, there are other major diseases or medical conditions that researchers think will significantly increase the risk and affect the treatment compliance or data interpretation;
12. Interventional treatment of other clinical trials within 4 weeks before screening.
13. Use Nidanib or pirfenidone for anti-fibrosis treatment within 8 weeks before screening;