Imipenem ( N-formimidoyl thienamycin): In vitro antimicrobial activity and β-lactamase stability

Abstract

In vitro studies with imipenem (N-formimidoyl thienamycin or MK0787) were performed with 8481 clinical isolates in three separate medical centers. More extensive comparative studies were also performed with 605 representative isolates, comparing imipenem to six other β-lactams. Although the newer β-lactams were often more active against susceptible species, imipenem demonstrated the broadest spectrum of antibacterial activity, with MIC 90s ≤ 4.0 μg/ml for all species tested except Pseudomonas maltophilia and P. cepacia . Imipenem was very active against all streptococci and staphylococci, in contrast to the third-generation cephalosporins. There was no evidence of cross-resistance between imipenem and the cephalosporins or penicillins. Resistance to hydrolysis by seven β-lactamase preparations was documented for imipenem, cefotaxime, and moxalactam. Like many other β-lactams, imipenem inhibited the Type I β-lactamase produced by Enterobacter cloacae . Other β-lactamases from gramnegative bacilli were also inhibited by high concentrations of imipenem.