International collaborative study on standardization of bacterial sensitivity to fosfomycin

An international collaborative study was undertaken involving 6 working groups to correlate the zone sizes obtained with 50 micrograms fosfomycin + 25 micrograms glucose-6-micrograms glucose-6-phosphate (G6P) and 50 micrograms fosfomycin + 50 micrograms G6P/disc with the MICs in the presence of 25 mg G6P/litre. The recommendations of the ICS for the MIC and disc diffusion methods were followed and Oxoid Mueller-Hinton agar was used. The regression lines obtained with the method of least squares show that the best correlation coefficient (r = 0.8227) corresponds to the disc with 50 micrograms fosfomycin + 50 micrograms G6P. Considering both the pharmacokinetics of fosfomycin after intravenous administration of 2 or 4 g and the distribution of sensitive bacterial populations, two breakpoints were established at MIC values of 16 and 64 mg/l corresponding to zone sizes and 18 and 22 mm, respectively.