In vitro activity of doripenem plus fosfomycin against drug-resistant clinical blood isolates.

The in vitro activity of doripenem in combination with fosfomycin was evaluated against a wide range of clinical blood isolates. Bacterial isolates of methicillin-resistant Staphylococcus aureus (MRSA; n = 39), Pseudomonas aeruginosa (n = 18), multidrug-resistant Escherichia coli (n = 10), Enterobacter cloacae (n = 3) and Klebsiella pneumoniae (n = 5) were investigated. For synergism testing the checkerboard test was applied and determined by calculation of the fractional inhibitory concentration index. Checkerboard results were verified by time-kill curve tests on selected isolates. Among MRSA, E. coli and K. pneumoniae, 94.9, 80 and 100% of isolates demonstrated synergism, respectively. Selected isolates demonstrated synergism in time-kill curve tests. P. aeruginosa isolates demonstrated no interaction in all isolates. Doripenem plus fosfomycin shows high efficacy with promising results in vitro.