Combined topical use of silver sulfadiazine and antibiotics as a possible solution to bacterial resistance in burn wounds

The superior efficacy of quinolones (norfloxacin, pefloxacin, and enoxacin) in controlling burn wound infections signals the discovery of new topical agents. However, there are a few reports on the emergence of resistant mutants to quinolones. Since attempts to develop AgSD resistant strains in vitro were unsuccessful and the emergence of AgSD resistance in vivo is a rare occurrence, we decided to investigate if the combined use of AgSD with other effective antibiotics, especially quinolones, would minimize the development of resistant bacteria. Our in vitro results indicate that when Ps. aeruginosa cultures were serially transferred 10 times through subinhibitory concentrations of norfloxacin, pefloxacin, etc., the MIC increased 40 times while when the cultures were passed through a combination of AgSD and these quinolones, the MIC of quinolones increased only tenfold. In vivo, when burned mice infected with either AgSD sensitive or resistant Ps. aeruginosa strains were treated with a topical cream containing 10mM silver sulfadiazine and 5mM norfloxacin or 5mM pefloxacin, the mortality was much lower than that of 10mM silver sulfadiazine alone or 5mM quinolones alone. Thus, combined use of silver sulfadiazine and quinolones appears to diminish the ability of Ps. aeruginosa strains to form resistant mutants. Furthermore, when the combination is used as a topical agent in burn wounds, lesser amounts of the individual drug are needed to control infection thereby reducing the toxic effects, if any, associated with these drugs. This combination does not in any way interfere with the antifungal or antibacterial properties of these individual drugs.