Clinical and economic implications of antimicrobial resistance for the management of community-acquired respiratory tract infections.

Lower respiratory tract infections (RTIs), particularly community-acquired pneumonia (CAP), account for over 50 million deaths annually worldwide. They place an extensive clinical and financial burden on healthcare authorities. Upper RTIs, usually mild and non-life threatening, also incur significant healthcare costs. The rising prevalence of resistance of the major causative agents of CAP (Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis) to beta-lactam antimicrobials and newer macrolides has necessitated new strategies for appropriate antimicrobial usage. A successful clinical outcome will depend on the patient, choice of drug, and the epidemiology and resistance of the pathogen. Treatment failure will result in increased costs, particularly if hospitalization is required. Pharmacokinetic and pharmacodynamic parameters are being used increasingly to predict maximally effective therapy and optimal bacterial eradication, thus limiting the development of resistance. Antimicrobial susceptibility criteria by MIC should be dictated by the type and location of the infection. Modifying the current MIC breakpoints for penicillin so that more pneumococcal pneumonia isolates are reported appropriately as being susceptible may lead to a decrease in the use of broad-spectrum antimicrobial therapy and its associated increased costs, in favour of more narrow-spectrum therapy. Targeting the pathogen with the most effective antimicrobial in an appropriately selected patient should optimize clinical and microbiological success and, consequently, maximize response rates and economic outcomes. In addition, research efforts need to concentrate on developing new agents with low propensity to select for or induce resistance.