Using an index-based approach to assess the population-level appropriateness of empirical antibiotic therapy

Abstract

Objectives: The population-level appropriateness of empirical antibiotic therapy can be conventionally measured by ascertainment of treatment coverage. This method involves a complex resource-intensive case-by-case assessment of the prescribed antibiotic treatment and the resistance of the causative microorganism. We aimed to develop an alternative approach based, instead, on the use of routinely available surveillance data.

Methods: We calculated a drug effectiveness index by combining three simple aggregated metrics: relative frequency of aetiological agents, level of resistance and relative frequency of antibiotic use. To evaluate the applicability of our approach, we used this metric to estimate the population-level appropriateness of guideline-compliant and non-guideline-compliant empirical treatment regimens in the context of the Dutch national guidelines for complicated urinary tract infections.

Results: The drug effectiveness index agrees within 5% with results obtained with the conventional approach based on a case-by-case ascertainment of treatment coverage. Additionally, we estimated that the appropriateness of 2008 antibiotic prescribing regimens would have declined by up to 4% by year 2011 in the Netherlands due to the emergence and expansion of antibiotic resistance.

Conclusions: The index-based framework can be an alternative approach to the estimation of point values and counterfactual trends in population-level empirical treatment appropriateness. In resource-constrained settings, where empirical prescribing is most prevalent and comprehensive studies to directly measure appropriateness may not be a practical proposition, an index-based approach could provide useful information to aid in the development and monitoring of antibiotic prescription guidelines.

Keywords: antimicrobial resistance; prescription guidelines; surveillance.

Figure 1.

Aetiological fractions: fraction of cases caused by each of the nine indicator bacterial species among patients in each UTI diagnosis group. Diagnostic group 1 corresponds to urosepsis/pyelonephritis/complicated UTI and diagnostic group 2 corresponds to complicated UTI associated with catheter use for >10 days. Results were obtained using cases from which a single bacterial species was isolated. Note the split y-axis.

Figure 2.

Resistance patterns: fraction of isolates collected in the UTI study that were characterized as resistant to each of the 20 antibiotic regimens considered in this study (see Table 1). × represents intrinsic resistance. Each panel corresponds to a different indicator bacterial species.

Figure 3.

Prescription patterns: relative frequency of patients treated with each of the 20 antibiotic regimens considered in this study (see Table 1). Each panel corresponds to a different diagnostic group/SWAB-compliance combination. Diagnostic group 1 corresponds to urosepsis/pyelonephritis/complicated UTI and diagnostic group 2 corresponds to complicated UTI associated with catheter use for >10 days.