In vitro activity of the newer quinolones compared with the classic ones and tobramycin.

The halogenated substitution of quinolone derivatives has given rise to a new group of substances called newer quinolones, which possess extraordinary antibacterial activity in vitro. The aim of our study was to compare the effect of the newer quinolones ciprofloxacin (CIP), norfloxacin (NOR) and enoxacin (ENO) with that of the classical ones nalidixic acid (NA), oxolinic acid (OX) and pipemidic acid (PIP) and with a widely-used aminoglycoside tobramycin (TBR). This was tested on 2,263 strains from clinical isolations. Evaluating the effect of the least active substances as a unit, we generally found the MIC90s to be of the following order: (Formula: see text). The remaining groups among the antibiotics studied are ordered identically, the most potent being the newer quinolones in the following order: CIP is at least four times superior to NOR, which in turn is at least twice as effective as ENO for gram-positive organisms, but only 1.2 times for gram-negative bacilli.