Analytical approach:
A mathematical model was used to estimate the sensitivity of bacteria to the antibiotic as a function of other relevant factors, such as the distribution of prescriptions (number treated), initial resistance, spontaneous rate of clearance, and rate of clearance with treatment. These data were then integrated into a decision tree to evaluate the cost-effectiveness of treatments at several time points (one, 15, 30, 45, and 60 months from treatment). The authors did not state the perspective.
Effectiveness data:
The clinical estimates included response, second-line antibiotic efficacy, antimicrobial resistance, and mortality. These data were primarily from a randomised controlled trial (Solomkin, et al. 2003, see ‘Other Publications of Related Interest’ below for bibliographic details). An alternative scenario was assessed that included
Escherichia coli (
E. coli) anti-microbial resistance, based on data from the European Study for Monitoring Antimicrobial Resistance Trends (SMART, Gallagher, et al. 2005, see ‘Other Publications of Related Interest’ below for bibliographic details). The primary clinical outcomes included treatment efficacy and life expectancy.
Monetary benefit and utility valuations:
The authors’ assumed that the disutility value, for the life-years expected when a patient survived an episode of intra-abdominal infection, was zero and this meant that discounted life-years were equal to discounted quality-adjusted life-years (QALYs).
Measure of benefit:
The measure of benefit was QALYs and they were discounted at 1.5% per year.
Cost data:
The types of resources, in the cost analysis, were the antibiotic agents (first-line and second-line), hospitalisation days, out-patient visits, and surgical intervention. The mean costs and ranges of values were presented for each of these four categories. The resource quantities were from three published studies (Solomkin, et al. 2003, Krobot, et al. 2004, and Davey, et al. 2001, see 'Other Publications of Related Interest' below for bibliographic details), and kostenhandleiding CVZ. The unit costs were from medicijnkosten.nl and kostenhandleiding CVZ, and the cost of surgical interventions was from Danish diagnosis-related group data (DBC). All costs were in Euros (EUR) and the price year was 2006. Values were adjusted for inflation and discounted at 4% per annum.
Analysis of uncertainty:
Two alternative scenarios were assessed, using
E. coli resistance data from the SMART (Gallagher, et al. 2005) and different initial efficacy data. Parameter uncertainty was assessed in one-way sensitivity analyses of all the modelled values. Probabilistic sensitivity analyses were used to measure the uncertainty in all parameters simultaneously, with beta distributions for dose, treatment duration, and efficacy, and triangular distributions for costs. Cost-effectiveness acceptability curves were created to illustrate these results.