Comparative efficacy of oral and intravenous cyclophosphamide in the treatment of connective tissue disease-associated interstitial lung disease and analysis of its influencing factors: a clinical trial

Introduction: Connective tissue disease (CTD) commonly affects the lungs, with interstitial lung disease (ILD) as its main complication; although cyclophosphamide (CTX) is the standard immunosuppressant for CTD-ILD, the optimal route of administration (oral vs. intravenous) remains unclear. This research aimed to analyze the efficacy of oral and intravenous CTX in the treatment of CTD-ILD and analysis of its influencing factors. Methods: The CTX per oral group (PO group) and intravenous infusion of CTX group (IV group) were established. Clinical efficacy, pulmonary function indices, pulmonary HRCT scores, blood gas parameters, 6-minute walking distance (6MWD), SGRQ scores, serum levels of KL-6, 25(OH)D, IFN-γ, and IL-4, and adverse reactions, were examined. Relevant factors influencing the clinical efficacy of CTD-ILD were analyzed. Results: After treatment, patients in the IV group exhibited lower HRCT score, SGRQ scores, and serum levels of KL-6 and IL-4 compared to those in the PO group. Conversely, the IV group had higher levels of FVC, FEV1, DLCO, FEV1/FVC ratio, PaO2, 6MWD, 25(OH)D, and IFN-γ. Higher serum levels of KL-6 and lower levels of 25(OH)D were associated with poorer treatment outcomes. Conclusion: For patients with CTD-ILD, intravenous infusion of CTX for 12 months demonstrates superior efficacy compared to oral administration, with a lower incidence of adverse reactions.