Nintedanib With or Without Dextromethorphan in Patients With Idiopathic Pulmonary Fibrosis (IPF)

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;