Abstract
BACKGROUND: Retrospective observational studies may provide real-world evidence about long-acting muscarinic receptor antagonist (LAMA) effectiveness in reducing mortality or COPD-related readmission risk after a COPD hospitalization. Causal inference and competing risk statistical procedures aid in managing confounding and competing outcome events that complicate retrospective analyses. OBJECTIVE: To compare COPD-related readmission and mortality risk among patients receiving a LAMA versus patients receiving no long-acting bronchodilator ("no LABD") within 30 days post-discharge. METHODS: This retrospective observational analysis of patients (aged ≥ 40 years) hospitalized for COPD used claims data (years 2004-2012). Events occurring during the period from 31 days through 12 months post-discharge were compared. The hazard ratio (HR) for the combined outcome of COPD-related readmission or mortality was estimated using Cox regression. Confounding was addressed using inverse probability of treatment weighting (IPTW). The competing risk of non-COPD-related readmission was considered. RESULTS: 10,405 COPD patients were included (LAMA = 751, no LABD = 9654). IPTW achieved a balanced sample (10,518 LAMA, 10,405 no LABD). Unweighted HR (LAMA vs no LABD) for COPD-related readmission or death, adjusted for age, sex, comorbidities, and baseline utilization, was 1.00 [95% confidence interval (CI) 0.84, 1.20]. Weighted (IPTW) adjusted HR was 0.94 (95% CI 0.88, 1.00). Unweighted and weighted HRs further adjusted for competing risk were 0.97 (95% CI 0.82, 1.16) and 0.91 (0.86, 0.98), respectively. CONCLUSIONS: Bias by indication and comorbidities make the measurement of retrospective COPD treatment effectiveness difficult. Using IPTW and additionally considering the competing event risk, LAMA use was associated with a small reduction in risk for COPD-related readmission or death over the period from 31 days to 12 months post-discharge.