Meropenem: a microbiological overview.

Meropenem is a parenteral carbapenem antibiotic which has excellent bactericidal activity in vitro against almost all clinically significant aerobes and anaerobes. Its high activity is explained by ease of entry into bacteria combined with good affinity for essential penicillin binding proteins, including those associated with cell lysis. Breadth of spectrum is due, in part, to stability to all serine-based beta-lactamases, including those which hydrolyse third-generation cephalosporins. Meropenem has an antibacterial spectrum which is broadly similar to that of imipenem but, whilst slightly less active against staphylococci and enterococci, it is more active against Pseudomonas aeruginosa, all Enterobacteriaceae and Haemophilus influenzae. Amongst common human pathogens, only methicillin-resistant staphylococci and Enterococcus faecium are uniformly resistant to meropenem. The meropenem MICs for penicillin-resistant Streptococcus pneumoniae are higher than for penicillin-susceptible strains but the organisms remain susceptible. Clinical susceptibility in vitro to meropenem is defined by MICs of < or = 4 mg/L, intermediate susceptibility by MICs of 8 mg/L and MICs of > or = 16 mg/L define resistance; equivalent figures for zones of growth inhibition are > or = 14 (susceptible), 12-13 (intermediate) and < or = 11 (resistant) mm. Studies in guinea pig models of systemic infection and infections localised to the lungs, urinary tract and the central nervous system, some of which used immunocompromised animals, confirm the potential of meropenem demonstrated in vitro. These factors, combined with the human plasma, tissue or urinary concentrations of meropenem which exceed modal MICs for the pathogens isolated in clinical trials for most or all of the recommended 8 h dosing interval, predict that meropenem should be efficacious in the treatment of infections at many body sites.