[Variations in vitro of the efficacy of quinolones as a function of pH]

pH induced changes of bacteriostatic activity of nalidixic, pipemidic and oxolinic acids have been studied in vitro by the determination of minimal inhibitory concentrations (MIC), on 9 different species and 172 strains, at pH 5, 6, 7 and 8 and with increasing antibiotic concentrations. The bacteriostatic activity of nalidixic acid is higher at acid pH and conversely the bacteriostatic effects of pipemidic and oxolinic acids are enhanced at basic pH. The relationship between pH and MIC seems to be more dependent on the type of the micro-organism than on the antibiotic which is tested. A study of the bactericidal effect of quinolones on E. Coli and Pr. Morganii has shown a sharp increase of bactericidal activity at basic pH. These results support the idea that alkalinization is a useful addition to the treatment of severe urinary infections by quinolones.