The antimicrobial and bactericidal activity of PC-904, a new semisynthetic penicillin synthesized in the laboratory of Sumitomo Chemical Co. Ltd., were examined using various species of clinical isolates. The results are summarized as follows.
(1) PC-904 was active against almost all of gram-negative bacilli as well as gram-positive organisms, superior to ABPC or CBPC. This agent showed potent activity especially against Pseudomonas aeruginosa, Ps.cepacia, Escherichia coli and Proteus species.
(2) PC-904 was active against ABPC-resistant Enterobacteriaceae and CBPC-resistant Ps.aeruginosa. It showed no cross-resistance with GM.
(3) The antibacterial and bactericidal activities were, in some cases, influenced by the inoculum size. The inoculum size effect showed good correlationship with the specific activity of beta-lactamase produced. PC-904 acted bactericidally in low inoculum.
(4) PC-904 was resistant to hydrolysis by cephalosporinase as well as ABPC. But, it was hydrolyzed by penicillinase and its relative rate of hydrolysis was similiar to that of ABPC, except for a part of type IV penicillinase, against which PC-904 was relatively resistant.
(5) PC-904 was more effective than CBPC against infections with E.coli, K.pneumoniae and Ps.aeruginosa in mice.