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 high-resolution computed tomography (HRCT) scores, blood gas parameters, 6-min walking distance (6MWD), SGRQ scores, serum levels of Krebs von den Lungen-6 (KL-6), 25-hydroxyvitamin D (25(OH)D), interferon-gamma (IFN-γ), and interleukin-4 (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 forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), diffusion capacity of the lung for carbon monoxide, FEV1/FVC ratio, partial pressure of oxygen, 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.