An integrated pharmacoeconomic approach to antimicrobial formulary decision-making.

Purpose: The utility of a novel interdisciplinary approach to antimicrobial formulary decision-making was studied.

Methods: Pseudomonas aeruginosa minimum inhibitory concentration (MIC) distribution data for cefepime and ceftazidime were retrieved from nonrepeat isolates obtained from November 2002 to October 2003. Unbound drug exposures were simulated for 5000 patients using the Monte Carlo method. Weighted target attainment rates (TARs) were calculated for cefepime and ceftazidime 1 g every 8 hours and 1 g every 12 hours (infused over 0.5, 2, and 4 hours), using three representative pharmacodynamic targets (percentage of time above the MIC of 67%, 100%, and 400%).

Results: MIC data for 1230 nonrepeat P. aeruginosa were analyzed. The MIC at which 90% of the P. aeruginosa isolates were inhibited was 16 and 32 mg/L for cefepime and ceftazidime, respectively. Drug acquisition cost was the highest with cefepime 1 g given every 8 hours (37.56 dollars/day), followed by cefepime 1 g every 12 hours (25.04 dollars/day) and ceftazidime 1 g every 8 hours (22.26 dollars/day). When infused over 0.5 hour, the highest TAR was achieved with cefepime 1 g every 8 hours (82%), followed by ceftazidime 1 g every 8 hours (77%) and cefepime 1 g every 12 hours (66%); ceftazidime 1 g every 8 hours was 70% more cost-effective than cefepime 1 g every 8 hours. Cefepime 1 g every 12 hours, infused over 4 hours, increased the TAR to 89% and was similar in cost-effectiveness to ceftazidime 1 g every 8 hours infused over 0.5 hour.

Conclusion: An integrated pharmacoeconomic approach to antimicrobial formulary decision-making addressed local resistance patterns, population pharmacokinetics, pharmacodynamics, dosing regimens, and drug acquisition costs. This method appeared to be more realistic and objective than the conventional approach of considering only drug acquisition costs, especially for agents in a similar structural or functional class.