Sulfadiazine silver-resistant Pseudomonas in Burns. New topical agents

Sulfadiazine silver-resistant strains of Pseudomonas aeruginosa isolated from burned patients from several countries are sensitive to sulfadiazine silver in vitro, but in burned mice and rats resist topical therapy with sulfadiazine silver. In searching for an effective topical agent against these resistant organisms, we found that FPQC (1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7[1-piperazinyl]-quinoline-carboxylic acid) and its silver salt are effective both in vitro and in vivo. In vitro, their minimal inhibitory concentrations are ten to 20 times lower than that of sulfadiazine silver. In burned mice infected with resistant Pseudomonas strains, mortality in groups receiving topical therapy with FPQC or FPQC silver is 0%, but 80% to 100% with sulfadiazine silver and 100% without treatment. Similar results were obtained in burned rats. The efficacy of FPQC and FPQC silver in vivo may represent discovery of new agents of known low toxicity that are useful in topical burn therapy.