We found that utilization of antibiotics increased in response to reductions in out-of-pocket price post Part D. However, it is difficult to discern whether these increases represent appropriate use, inappropriate use or some combination of both, because we cannot accurately assess the quality of antibiotic prescribing using insurance claims data. For pneumonia, we found Part D was associated with a triple increase in rates of antibiotic treatment among those previously lacking drug coverage, with a relative odds ratio of 3.60 (95% CI 2.35–5.53), after adjusting for secular trends in the comparison group. Given the high mortality associated with community-acquired pneumonia among the elderly,22
the finding that changes in drug coverage improve the likelihood of treatment is encouraging.
However, we also found increases in antibiotic use for other acute respiratory infections (sinusitis, pharyngitis, bronchitis, and nonspecific upper respiratory tract infection) for which antibiotics are generally not indicated.18
We found rates of antibiotic use for ARIs declined between 2004–2005 and 2006–2007 for the group whose drug coverage did not change. In contrast, the three groups who moved from limited or no drug coverage to Part D increased their use of antibiotics for ARIs. The magnitude of these increases was smaller than that for pneumonia. Inappropriate use of antibiotics has contributed to the development of antibiotic-resistant bacteria and has as a result been the target of numerous interventions to reduce use.3
Our findings suggest that changes in drug coverage among the elderly may exacerbate problems with antibiotic overuse.
Increased antibiotic prescription fill rates may be explained by a change in patient behavior, physician behavior or by some combination. Patients with generous drug coverage may be more likely to request an antibiotic prescription and more likely to fill it. Likewise, surveys suggest physicians’ decisions about whether and what to prescribe may be influenced by their perceptions about their patient’s ability to pay for drugs although communication between older adults and physicians about drug cost burden is known to be inadequate.23, 24
Systematic reviews suggest that more complex, multifaceted interventions are more effective at reducing inappropriate antibiotic prescribing.3, 4
Our findings suggest that health systems may consider changes to patient cost-sharing as another potential lever to alter patient and provider behavior.
We also found different responses to changes in drug coverage across antibiotic subclasses. While the group transitioning from no or limited coverage to Part D increased use of nearly all antibiotics (with the exception of sulfonamides), they increased use of broad spectrum antibiotics (e.g., macrolides and quinolones), more so than other older, cheaper subclasses. We expected a larger effect of insurance coverage changes for these subclasses which can cost up to $30 per day compared to less than $1 per day of treatment for older classes such as penicillin (authors’ calculation based on average costs in our study sample). This might be a concern because broad-spectrum antibiotics generally are more likely to lead to bacterial resistance.25
Our study is subject to certain limitations. First, because the individuals we studied were all enrolled in MA-PD plans offered from one insurance company, the results might not generalize to all older adults. Second, our results are based on drugs purchased at network pharmacies, but any bias from missing claims is likely negligible for several reasons. For the time period in which beneficiaries paid entirely out-of-pocket those using a network pharmacy received a 15% discount from the plan’s negotiated prices which were already well below a retail price. In addition, network pharmacies were numerous and covered almost all local pharmacies. Third, we could not distinguish between bacterial and viral pneumonia using claims data. Antibiotics are not indicated for viral pneumonia. However, our pre-post-with-comparison-group approach should control for temporal trends in viral and/or bacterial pneumonia that affect study groups and we do not expect differences across study groups in the underlying causes of pneumonia. Similarly, we are not able to determine from claims data whether or not the use of broad spectrum antibiotics is appropriate.
In sum, use of antibiotics increased as individuals gained better drug coverage, especially for broad-spectrum, newer and more expensive, antibiotics. We found increases in the likelihood of antibiotic treatment for both pneumonia and other ARIs. These increases took place against a backdrop of declines in antibiotics overall nationally.5
Our study suggests that reimbursement may play a role in addressing the substantial role of inappropriate antibiotic prescribing and use.