Samy Suissa, PhD; Pierre Ernst, MD, MSc
Potential Financial Conflicts of Interest:Grants received: S. Suissa (AstraZeneca, Boehringer Ingelheim, GlaxoSmithKline, Pfizer), P. Ernst (AstraZeneca, GlaxoSmithKline, Novartis, Merck & Co., Nycomed).
Suissa S., Ernst P.; How Much Did Biases in the Study of Chronic Obstructive Pulmonary Disease Medications and Mortality Affect the Outcome?. Ann Intern Med. 2009;150:425-426. doi: 10.7326/0003-4819-150-6-200903170-00017
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Published: Ann Intern Med. 2009;150(6):425-426.
TO THE EDITOR:
Lee and colleagues (1), using an observational study design, report that the use of ipratropium is associated with a 34% increase in the risk for cardiovascular death and that the use of inhaled corticosteroids (ICSs) is associated with a 20% reduction in all-cause mortality in patients with chronic obstructive pulmonary disease (COPD). Some methodological considerations should be addressed in judging the validity of these findings.
The excess risk for cardiovascular death seen with ipratropium (odds ratio, 1.34 [95% CI, 1.22 to 1.47]) may be due to the marked imbalance between case patients and control participants in the occurrence of COPD exacerbations during the previous 6 months (64% and 22%, respectively) (2). Although the data analysis adjusted the odds ratio downward from 1.75 (crude) to 1.34, the statistical approach did not consider the timing of the exacerbation and thus could not distinguish whether the cardiac outcomes occur through the increased likelihood of an exacerbation or whether they require the occurrence of an exacerbation. A more refined analysis, one that can account for the timing of exacerbations relative to the timing of ipratropium use, could further reduce the adjusted risk.
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