In vitro and in vivo activities of meropenem and comparable antimicrobial agents against Haemophilus influenzae, including β-lactamase-negative ampicillin-resistant strains

The in vitro activity of ampicillin, cefotaxime, meropenem, panipenem, imipenem and biapenem was assayed using ampicillin-susceptible, beta -lactamase-positive and beta -lactamase-negative ampicillin-resistant (BLNAR) Haemophilus influenzae isolated recently in Japan. Against ampicillin-susceptible isolates, cefotaxime was the most potent (MIC90 0.016 mg/mL). Both cefotaxime and meropenem (MIC90 of both, 0.5 mg/L) were the most potent against beta -lactamase-positive isolates. Against BLNAR isolates, meropenem (MIC90 0.5 mg/L) was the most potent. In murine bronchopneumonia caused by ampicillin-susceptible and BLNAR H. influenzae, cefotaxime showed the best efficacy, followed by meropenem. Our results indicate that meropenem could be a useful intravenous agent for infections caused by H. influenzae, including BLNAR strains.