In vitro antimicrobial activity of sulbactam·ampicillin and its therapeutic efficacy in lower respiratory infections

We examined the in vitro antimicrobial activity of sulbactam. ampicillin (SBT·ABPC), a 2:1 composition of ABPC and SBT, a potent inhibitor of β-lactamases, by a microbroth dilution method using the Dynatech MIC-2000 system, and evaluated its therapeutic effect in lower respiratory infections. The minimum inhibitory concentrations (MICs) of SBT·ABPC, ABPC, piperacillin (PIPC) and cefazolin (CEZ) against the following 155 clinical isolates were determined: 20 strains each of S. aureus, E. coil, K. pneumoniae, E. cloacae, S. marcescens and P. aeruginosa, 25 strains of H. influenzae and 10 strains of B. catarrhalls. The determination of MICs showed that SBT·ABPC was more active against all the species, especially against β-lactamase-producing strains such as B. catarrhalis, K. pneumoniae and ABPC-resistant S. aureus, H. influenzae, E. coli and E. cloacae, than ABPC. A daily dose of 3 to 6 g of SBT·ABPC was given by drip infusion to 10 patients: 4 with pneumonia, 2 with chronic respiratory infection and 4 with infection in association with lung cancer. Clinical effect was good in 7 and poor in 2. One patient with diffuse panbronchiolitis was excluded from the clinical evaluation. Five strains that were identified as causative organisms were all eradicated by SBT ABPC. Drug-induced fever and eosinophilia were observed in one patient each. The adverse reactions disappeared after completion of the therapy. From the above results, we conclude that SBT·ABPC is most useful as a first choice antibiotic for the treatment of lower respiratory infections.