Preadmission Adherence to Inhaled Maintenance Therapy and Antibiotic Treatment Duration in Patients with COPD Hospitalized for Pneumonia is Associated with Reduced Antibiotic Exposure and Improved Clinical Outcomes in COPD and Pneumonia: A Retrospective Cohort Study.

Aim: To examine the associations between pre-admission adherence to inhaled maintenance therapy and in-hospital antibiotic treatment duration and clinical outcomes among patients with chronic obstructive pulmonary disease (COPD) hospitalized for pneumonia. Methods: This single-center retrospective cohort (July 2022-July 2025) included 250 patients with COPD and pneumonia. Adherence during the preceding 12 months was assessed using the proportion of days covered (PDC). Patients were classified into high-adherence (PDC ≥80%, n = 96) and low-adherence (PDC <80%, n = 154) groups. The primary outcome was antibiotic treatment duration. Multivariable regression and propensity score matching (PSM) were used to evaluate the associations. Results: Higher adherence was associated with shorter antibiotic treatment duration in the multivariable analysis (β = -1.589 days, 95% CI: -2.390 to -0.789; P < 0.001). This association remained statistically significant after PSM (76 matched pairs; β = -1.421 days, 95% CI: -2.372 to -0.470; P = 0.003). Associations with shorter time to clinical stability, shorter hospitalization, and lower hospital costs were also observed in the adjusted and matched analyses. However, associations with antibiotic escalation, treatment failure, and readmission were not statistically significant after matching. Conclusion: Higher pre-admission adherence to inhaled maintenance therapy was consistently associated with shorter antibiotic treatment duration among patients with COPD hospitalized for pneumonia. Associations with selected continuous clinical outcomes were also observed, whereas evidence for secondary binary outcomes was less conclusive. These observational findings do not establish causality.