N-Formimidoyl thienamycin (MK0787): in-vitro antibacterial activity and susceptibility to beta-lactamases compared with that of cefotaxime, moxalactam and other beta-lactam antibiotics

Abstract

The in-vitro activity of N-formimidoyl thienamycin was assessed against recent clinical isolates of common bacteria and also against reference strains that produced known β-lactamases. The compound was highly active against most streptococci and staphylococci, though enterococci and penicillin-resistant pneumococci were less sensitive, as were methicillin-resistant staphylococci especially when a large inoculum was tested. It was active against Acinetobacter spp., Pseudomonas aeruginosa and other pseudomonads except Ps. maltophilia. The compound was also active against enterobacteria but less so than cefotaxime or moxalactam against most isolates; however, Proteus spp. and Providencia spp. were less sensitive than other enterobacteria. N-Formimidoyl thienamycin was active against gonococci, though less so than cefotaxime, and also against Haemophilus influenzae, though against this organism its activity was exceeded by that of cefotaxime, moxalactam and ampicillin. Most anaerobes, including members of the Bacteroides fragilis group, were sensitive to the compound but some clostridia, including isolates of Clostridium difficile, were resistant. Although the compound was highly resistant to β-lactamases it was hydrolysed by a few enzymes, albeit very slowly.