Influence of storage and susceptibility test conditions on stability and activity of LY163892 and four other cephalosporins

A new carbacephem analog of cefaclor, LY163892, was examined along with four other cephalosporins for chemical stability and for antibacterial activity under a variety of susceptibility test conditions. LY163892 was found to be markedly more stable than cefaclor during storage at 4 and 35 degrees C in human serum, human urine, and various bacteriological media. Under these conditions, LY163892 demonstrated stability equal or superior to the stabilities of cephalexin, cephalothin, and cefuroxime. Broth and agar dilution susceptibility tests did not reveal significant differences in LY163892 activity in a variety of test media, although LY163892 MICs were somewhat higher in Mueller-Hinton chocolate agar or Trypticase soy broth (BBL Microbiology Systems, Cockeysville, Md.) than in other media. The activity of LY163892 against selected pathogens was only slightly influenced by the increased or decreased pH of the test medium, in a manner similar to that of the other cephalosporins tested. Thus, the carbacephem structure of LY163892 appears to represent a more stable cephalosporin than cefaclor, while retaining a similar antimicrobial spectrum.