Clinical and laboratory studies were performed on SBTPC (mutual prodrug of SBT and ABPC). MICs of SBTPC against 551 clinically isolated strains were measured, and compared with those of ABPC. Against Gram positive cocci ABPC was superior by one grade to SBTPC. Against Shigella, Salmonella, Citrobacter, Enterobacter, Hemophilus, P. mirabilis, P. rettgeri and P. inconstans the same results as to Gram-positive cocci were obtained. Against K. pneumoniae, K. oxytoca, P. vulgaris, P. morganii,

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... bacter, V. parahemolyticus and Plesiomonas SBTPC was superior to ABPC. Against Serratia and P. maltophilia both drug showed the same pattern in MIC distribution. Against ABPC resistant E. coil, SBTPC showed much stronger antimicrobial activity than ABPC. SBTPC was administered to two cases of respiratory tract infection, also two cases of urinary tract infection and a case of FUO. Good clinical results were obtained in the cases of urinary tract infection . As to adverse reaction, diarrhea in one case and the elevation of transaminase activity with eosinophilia in another case were observed .