Imipenem is a carbapenem antibiotic with an extremely broad spectrum of activity. It is combined with cilastatin, which is an inhibitor of dehydropeptidase, an inactivating enzyme of the renal brush border which ensures adequate urinary concentrations. Meropenem has similar activity but does not require an enzyme inhibitor. Both antibiotics are highly active against streptococci, but enterococci are less susceptible and methicillin-resistant staphylococci are resistant. Neisseria and Hemophilus species are susceptible, as are E. coli, Klebsiella species, and Salmonella species. Enterobacter species, Serratia species, Proteus species, and C. freundi are less susceptible. They have moderate activity against Pseudomonas species but Stenotrophomonas maltophilia is resistant. Bacteroides species, Fusobacterium species, and to a lesser extent Clostridium species are also susceptible. The carbapenems are inducers of b-lactamase and should not be combined with other b-lactams. Penetration is good into most tissues except the meninges. Excretion is predominantly renal.
The carbapenems are used when several antibiotics would otherwise have to be given. Bacteremia, severe respiratory or urinary infections, febrile neutropenic episodes, and abdominal sepsis are common indications. Pseudomonal infections are better treated with other agents. Nausea and vomiting are common and fits develop in 1 per cent of patients given imipenem. Patients allergic to penicillins may be allergic to carbapenems. Superinfection with resistant pseudomonads or fungi can develop.
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