Serum bactericidal activity of two newer quinolones against Salmonella typhi compared with standard therapeutic regimens.

The bactericidal activity of two newer quinolones, ciprofloxacin and ofloxacin, against eight strains of Salmonella typhi was examined by the serum dilution test and studies of bacterial killing kinetics in human serum, and compared to standard regimens. Bactericidal titers for ciprofloxacin ranged from 1:388 to 1:119 two hours and from 1:119 to 1:57 six hours after volunteers received an oral dose of 500 mg. The respective titers obtained after a 200 mg oral dose of ofloxacin were somewhat lower, but still exceeded 1:16 in all instances. Studies of bacterial killing kinetics demonstrated a rapid bactericidal action of both drugs against all strains tested. Compared to the classical anti-typhoid agents chloramphenicol, cotrimoxazole and amoxicillin, the new quinolones showed both markedly higher bactericidal titers and more rapid killing of Salmonella typhi in human serum.