In vitro testing of the antibacterial activity of fosfomycin trometamol against urinary pathogens.

The activity of fosfomycin trometamol (FOT) was compared with that of cotrimoxazole (COT) and norfloxacin (NOR) using urine as medium and 10(7) bacteria as inoculum, conditions as close as those found by the administration of the drugs in vivo during the course of a urinary tract infection. The minimum inhibitory concentrations (MIC) of all antibiotics against 100 strains isolated from urinary tract infections were found to be higher than the breakpoint. Concentrations of FOT corresponding to mean and maximal values found in urine after single dose administration within the 0-48 h interval killed the great majority of strains. COT and NOR, when tested under similar conditions, exhibited an antibacterial activity lower than and equal to that of FOT, respectively. In several strains belonging to different species the frequency of mutation to resistance to 2000 and 1000 micrograms/ml of FOT was very low (greater than 10(-7], whereas it was relatively high (1 x 10(-5) to 1 x 10(-7] for 150 micrograms/ml, the two former and the latter being the respective maximal, mean and minimal values found in urine after administration of a single dose.