A 2 X 2 factorial experiment of antibiotic concentration and pH on antibacterial activity of gentamicin in urine of low osmolality.

Two levels of gentamicin concentration (10 and 50 micrograms/ml were cross associated with two pH levels (pH 5 and 6) in a typical factorial arrangement of treatments. The time in hours required for the death of 50% (T50) of the inoculated microorganisms (E. coli and P. aeruginosa) was determined in urine of low osmolality (diabetes insipidus). Normal pH (pH 6) conserves its known favorable influence on gentamicin activity even at low osmolality. Interaction between pH and gentamicin concentration does exist at the 1% level but is antagonistic. The reasons are briefly discussed.