Microbiological basis for the use of fosfomycin trometamol as single-dose therapy for simple cystitis

Fosfomycin trometamol (FOT), a new soluble salt of fosfomycin, was developed especially for single-dose treatment in uncomplicated urinary tract infections. In this study, the minimum inhibitory concentrations (MICs) of FOT were measured both in nutrient broth and human urine and compared with calcium fosfomycin, pipemidic acid and cotrimoxazole. A total of 300 bacterial strains of different species from recent urinary infections were studied. Staphylococcus aureus showed the lowest MIC (0.38 micrograms/ml) and Pseudomonas spp. the highest (50 micrograms/ml) with fosfomycin salts in nutrient broth. The MIC of fosfomycin resulted in being higher than those for pipemidic acid and cotrimoxazole against Escherichia coli and Proteus rettgeri and lower for all the other species considered. The MIC values increased about ten times when urine was used as medium. No differences were observed between the two fosfomycin salts. The fosfomycin concentrations of 137-1500 micrograms/ml, easily obtained in urine of healthy adult subjects after a single dose of FOT (3g of fosfomycin), were able to kill all the strains, with the exception of Streptococcus faecalis. The bacterial adhesion of a resistant microorganism (P. aeruginosa) to the cells of the urinary tract, showed a 50% reduction after FOT treatment.