Objectives. To investigate the correlation between in vitro susceptibility of isolates and clinical outcomes with telithromycin in respiratory tract infections.

Methods. The activity of telithromycin was determined by in vitro susceptibility testing of key respiratory tract pathogens isolated from patients with community-acquired pneumonia, acute exacerbations of chronic bronchitis or acute maxillary sinusitis enrolled in 14 Phase III/IV clinical trials evaluating the clinical efficacy of telithromycin.

Results. In this pooled analysis, telithromycin mode minimum inhibitory concentration (MIC) and MIC₉₀, respectively, were: 0.016 and 0.03 mg/l against Streptococcus pneumoniae (n=626); 0.03 and 0.5 mg/l for penicillin-resistant S. pneumoniae (n=56); 0.03 and 1 mg/l for erythromycin-resistant S. pneumoniae (n=81); 2 and 4 mg/l against Haemophilus influenzae (including β-lactamase producers; n=627); both 0.12 mg/l for Moraxella catarrhalis (n=159); and both 0.25 mg/l for Staphylococcus aureus (n=124). Telithromycin (5 or 7–10 days) resulted in overall clinical and bacteriologic success rates of 88.1% (1593/1808) and 89% (1593/1789), respectively.

Conclusions. High levels of in vitro susceptibility to telithromycin are paralleled by high rates of clinical cure and bacteriologic eradication.