Background:

Telithromycin is a ketolide compound with proven, improved activity against Streptococcus pneumoniae isolates. However, its activity against Haemophilus influenzae isolates has been studied to a lesser extent. This study assessed the in vitro activity of telithromycin against recent H. influenzae isolates recovered from adult patients in Spain.

Material and Methods:

A total of 246 H. influenzae isolates obtained from adult patients (=16 years), one isolate per patient, suffering respiratory tract infections during the 2003 respiratory disease season were studied. Isolates were recovered from 10 Spanish hospitals in different geographic areas. Susceptibility testing was performed as recommended by the NCCLS using microdilution panels (Trek Diagnostic, UK).

Results:

Telithromycin activity (MIC range, MIC 50 and MIC 90: 0.25–16, 2 and 4 mg/mL, respectively) was similar to that of azithromycin (0.12–16, 1 and 2 mg/mL), and clearly higher than that of clarithromycin (0.5–64, 8 and 16 mg/mL) and erythromycin (0.5 to >32, 8 and 16 mg/mL). Using 4 and 16 mg/mL to define the susceptible and resistant category for telithromycin, 98.4 and 0.8% of isolates, respectively, were included within each category. The corresponding values within the susceptible category for azithromycin and clarithromycin using the NCCLS criteria (M100-S13) were 98.4% (4 mg/mL) and 68.3% (8 mg/mL), respectively. One isolate was resistant to azithromycin (MIC, 16 mg/mL) but susceptible to telithromycin (4 mg/mL) and two isolates were resistant to telithromycin (MIC, 16 mg/mL) but susceptible to azithromycin (4 mg/mL). These three isolates were resistant to clarithromycin (32–64 mg/mL). Overall b-lactamase production was 20%. Less than 3% of isolates were b-lactamase negative and resistant to ampicillin. It is of note that three (1.2%) isolates were resistant to amoxicillin/clavulanate (MIC, 8/4 mg/mL) and one (0.4%) isolate were resistant to levofloxacin (2 mg/mL), all remaining susceptible to telithromycin (MIC range, 1–2 mg/mL).

Conclusions:

In vitro telithromycin activity against H. influenzae isolates was comparable with azithromycin and higher than clarithromycin. Moreover, telithromycin was active against H. influenzae isolates with emerging resistance mechanisms to amoxicillin/clavulanate or fluoroquinolones.