In this paper, we found substantial variation in the use of antibiotics across regions at all levels, after adjusting for population characteristics. These regional differences did not appear to be simply explained by differences in the prevalence of the underlying conditions, since we found that regions with high utilization of antibiotics often had lower rates of diagnosis with pneumonia.
Compared with previous studies that examined geographic patterns of the use of all medications, we found that variation in the use of antibiotics was substantially larger.6, 8
For example, Zhang and colleagues found that the ratio of the 75th
percentile to the 25th
percentile for spending on all drugs at the HRR-level was 1.12. By contrast, the present study found that this ratio was 1.32 for antibiotics. Compared to studies that examined antibiotic use in the commercial population (children and younger adults <65), we found that the Medicare population (aged≥65) used more antibiotics, 1.10 per person per year in our sample compared to 0.88 per person per year in commercial population.11
In addition, the variation in utilization of antibiotics we found across states was similar to what Steinman and colleagues reported across commercial health plans.11
For example, a re-examination of their results show that the ratio of the 90th
percentile to the 10th
of prescription counts is approximately 1.50 across commercial plans. Our results show that the variation across US states is 1.42. Our findings show that the South had the highest utilization of antibiotics, consistent with previous studies both of antibiotic utilization11
and of overall prescribing quality (which found worse quality of prescribing in the South compared to other regions of the country).7
In addition to regional differences, we found significant patterns of seasonal variation in antibiotic use, with the highest utilization in the winter months. While rates of bacterial infection were also higher in these months, so were the rates of upper respiratory tract infections and acute respiratory tract infections. Since patients with these conditions are often prescribed antibiotics unnecessarily, it is likely that the rates of inappropriate use of antibiotics are also highest in the winter months.
There are several limitations of our data and methods. First, we have adjusted for observable patient characteristics, including demographics, insurance status and some clinical characteristics. However, we cannot fully adjust for disease severity and other discrete health status measures, or for a patient’s preferences and explicit requests and expectations for antibiotic treatment. These unadjusted factors could explain part of the variation we found. Second, we cannot directly measure appropriate and inappropriate use of antibiotics at the individual level because under-code and miscode for bacterial pneumonia and other acute respiratory tract infections in claims data are common.16
Instead, we examine this issue by determining whether regions that use more antibiotics have higher disease incidence. This is still subject to under-code and miscode but is less problematic, because we only examine the aggregated trend over time instead of measuring at the individual level. In addition, by looking at diagnosis independent of drug prescribing we reduce bias of upcoding when a diagnosis may be written to implicitly justify the decision to prescribe an antibiotic. We are simply demonstrating substantial variation in antibiotic use across regions. Variation described here suggests that inappropriate use of antibiotics in some regions and months might be higher than other regions and months, but it is difficult to know the right level of antibiotic use.
Despite these limitations, our study yields some important findings that have policy implications. Our study could be the first study using most recent national Medicare Part D data to evaluate geographic variation in outpatient antibiotic prescribing among older adults. Medicare Part D data is the most comprehensive dataset to examine national regional variation in antibiotic use because there are no other comparable national data. Although we do not have the data to directly address the degree to which results seen in Medicare patients extrapolate to younger patients, the findings in our study (e.g., higher rates of antibiotics in the south) are consistent with similar findings among younger adults. This suggests a possible correlation between prescribing behaviors for younger vs older adults.
In addition, it is important to examine antibiotic use in Medicare beneficiaries because older patients often have multiple comorbid conditions, which makes them more susceptible to complications and bad outcomes from untreated infections.17, 18
Consequently, there is an incentive for physicians to treat older patients more aggressively with antibiotics. On the other hand, older patients might be subject to more severe adverse outcomes of antibiotic use regardless of whether or not the antibiotic actually was indicated, including, for example, clostridium difficile colitis, cognitive disturbance with quinolones, and clinically significant drug-drug interactions.3–5
In addition, bacterial resistance is a societal concern. Thus, physicians should be extra careful to ensure not to prescribe unnecessary antibiotics to older patients. However, currently there is no quality measure that tracks the use of antibiotics among older adults – for example, the National Committee for Quality Assurance only tracks the antibiotic use among all children as well as avoidance of antibiotic treatment in adults younger than 65 with acute bronchitis, but not for older adults.19
Overall, areas with high rates of antibiotic use may benefit from more targeted programs to reduce unnecessary antibiotic use. Although the use in lowest-utilization region does not necessarily represent the clinically appropriate use, given that the overuse of antibiotics is common, quality improvement programs can be set at attainable targets using the low-prescribing areas (states in the West) as reference. In the past, quality measures looking at overuse of antibiotics have tended to shy away from older patients. Although older patients might have higher risk of adverse outcomes of infection, they may also be at particularly high risk of adverse outcomes of antibiotic use. Thus, it might be necessary to target some quality improvement initiates to this group.