Investigators have attributed protective effects of statins against pneumonia and other infections. However, these reports are based on observational data where treatments are not assigned randomly. We aimed to determine if the protective effects of statins against pneumonia are due to nonrandom treatment assignment.Methods.
We built a cohort consisting of 124 695 Medicare beneficiaries diagnosed with an acute myocardial infarction (AMI) for which we had complete claims data. We considered patients who survived at least 30 days post-AMI (full sample), or who survived for 1 year post-AMI (survivors). First, we used ordinary least squares (OLS) and logit models to determine if receiving a statin was protective against pneumonia. Second, to control for nonrandom treatment assignment, we performed an instrumental variables analysis using geographic treatment rates as an instrument. All models included patient demographics, medications, diagnoses, length of hospital stay, and out-ofpocket drug costs as covariates. Our outcome measure was a pneumonia diagnosis during the 1 year following AMI.Results.
A total of 76 994 patients (61.9%) filled a statin prescription, and 19 078 (15.3%) were diagnosed with pneumonia. Using OLS, the statin coefficient was -0.016 (P < .001), indicating that statins are associated with a reduction in pneumonia. Using instrumental variables, we find that statin prescriptions are not associated with a reduction in pneumonia. For the full sample, statin coefficients ranged from -0.001 to -0.01 (P > .6).Conclusions.
For patients with AMI, the protective effect of statins against pneumonia is most likely the result of nonrandom treatment assignment (ie, a healthy-user bias).