title: Antibiotic expected effectiveness and cost under real life microbiology: evaluation of ertapenem and ceftriaxone in the treatment of community-acquired pneumonia for elderly patients in Spain.
abstract: BACKGROUND
  Clinical efficacy of antibiotics may be affected by changes in the susceptibility of microorganisms to antimicrobial agents. The purpose of this study is to assess how these changes could affect the initial efficacy of ertapenem and ceftriaxone in the treatment of community-acquired pneumonia (CAP) in elderly patients and the potential consequences this may have in health care costs.
  
  
  METHODS
  Initial efficacy in elderly was obtained from a combined analysis of two multicenter, randomized studies. An alternative scenario was carried out using initial efficacy data according to the pneumonia severity index (PSI). Country-specific pathogens distribution was obtained from a national epidemiological study, and microbiological susceptibilities to first- and second-line therapies were obtained from Spanish or European surveillance studies. A decision analytic model was used to compare ertapenem versus ceftriaxone for CAP inpatient treatment. Inputs of the model were the expected effectiveness previously estimated and resource use considering a Spanish national health system perspective. Outcomes include difference in proportion of successfully treated patients and difference in total costs between ertapenem and ceftriaxone. The model performed one-way and probabilistic sensitivity analyses.
  
  
  RESULTS
  First-line treatment of CAP with ertapenem led to a higher proportion of successfully treated patients compared with ceftriaxone in Spain. One-way sensitivity analysis showed that length of stay was the key parameter of the model. Probabilistic sensitivity analysis showed that ertapenem can be a cost-saving strategy compared with ceftriaxone, with a 59% probability of being dominant (lower costs with additional health benefits) for both, elderly patients (>65 years) and patients with PSI >3.
  
  
  CONCLUSIONS
  The incorporation of the current antimicrobial susceptibility into the initial clinical efficacy has a significant impact in outcomes and costs in CAP treatment. The treatment with ertapenem compared with ceftriaxone resulted in better clinical outcomes and lower treatment costs for two segments of the Spanish population: elderly patients and patients with severe pneumonia (PSI >3).
authors.affiliation: Hospital del Mar, Barcelona, Spain.
authors.forename: Santiago
authors.initials: S
authors.lastname: Grau
authors.affiliation: Pharmacoeconomics and Outcomes Research Iberia, Madrid, Spain.
authors.forename: Virginia
authors.initials: V
authors.lastname: Lozano
authors.affiliation: Outcomes Research Merck Sharp and Dohme Ltd, Madrid, Spain.
authors.forename: Amparo
authors.initials: A
authors.lastname: Valladares
authors.affiliation: Medical Affairs, Merck Sharp and Dohme Ltd, Madrid, Spain.
authors.forename: Rafael
authors.initials: R
authors.lastname: Cavanillas
authors.affiliation: Global Health Outcomes, Merck Sharp and Dohme Ltd, Whitehouse Station, NJ, USA.
authors.forename: Yang
authors.initials: Y
authors.lastname: Xie
authors.affiliation: Outcomes Research Merck Sharp and Dohme Ltd, Madrid, Spain.
authors.forename: Gonzalo
authors.initials: G
authors.lastname: Nocea
keywords: Spain; aged; antibacterial agent; bacterial infection; cost-effectiveness analyses; drug costs