Evaluation of disk susceptibility testing of fosfomycin tromethamine.
Fosfomycin tromethamine is an orally administered fosfomycin that may be used for single-dose therapy of uncomplicated urinary tract infections. At breakpoint concentrations [< or = 128 micrograms/ml plus 25 micrograms/ml glucose-6-phosphate (G-6-P)], fosfomycin tromethamine inhibited > 90% of the 350 bacterial isolates tested. When testing Escherichia coli, Klebsiella spp., and Enterobacter spp., we note that the performance of fosfomycin disks improved when G-6-P was added to the disks. The interpretive error rates were minimized when 200-micrograms fosfomycin disks were supplemented with either 50 or 100 micrograms G-6-P. Using < or = 128 and > or = 256 micrograms/ml as the susceptible and resistant MIC breakpoints, respectively, the regression-analysis-derived disk diffusion zone diameter breakpoints for the 200-micrograms fosfomycin disk supplemented with 50 micrograms of G-6-P are as follows: susceptible, > or = 16 mm; intermediate, 13-15 mm; and resistant, < or = 12 mm.
Pfaller
M A
MA
Department of Pathology, Oregon Health Sciences University, Portland 97201.
Barry
A L
AL
Fuchs
P C
PC
D001419:Bacteria / Q000187:drug effects*; D005069:Evaluation Studies as Topic; D005578:Fosfomycin / Q000031:analogs & derivatives* / Q000494:pharmacology; D019298:Glucose-6-Phosphate; D005958:Glucosephosphates; D008826:Microbial Sensitivity Tests; D012044:Regression Analysis; D014325:Tromethamine / Q000031:analogs & derivatives* / Q000494:pharmacology; D014551:Urinary Tract / Q000382:microbiology
D005958:Glucosephosphates; D014325:Tromethamine; D005578:Fosfomycin; D019298:Glucose-6-Phosphate