Comparative in-vitro activity of a new oral carbacephem, LY163892.

The in-vitro activity of a new oral carbacephem, LY163892, was compared with cefaclor, cephalexin, cephradine, cefadroxil and selected penicillins against 529 bacterial isolates. LY163892 exhibited greater activity in vitro than all four cephalosporins against Haemophilus influenzae, beta-lactamase producing Branhamella catarrhalis, Escherichia coli, Klebsiella spp. and Proteus mirabilis. LY163892 had equivalent potency to cefaclor against non-beta-lactamase producing B. catarrhalis, streptococci and Staphylococcus aureus. Group D beta-haemolytic streptococci, Proteus vulgaris, and methicillin-resistant staphylococci were universally resistant to LY163892 and the four cephalosporins. Broth dilution experiments indicated that LY163892 was bactericidal against a range of Gram-positive and Gram-negative organisms and suggested that the antibiotic had a similar degree of stability to the beta-lactamases of H. influenzae, B. catarrhalis and Staph. aureus as did cefaclor. The susceptibility of 16 strains of H. influenzae to LY163892 and cefaclor were equivalent when estimated using three different commercially available agar media. Addition of carbon dioxide to the incubation atmosphere significantly reduced the potency of both drugs.