The present invention relates to methods of inhibiting the proliferation of a microbial population of a surface lesion of a human or animal, wherein the lesion is contacted with an antimicrobial composition comprising a pharmaceutically acceptable antibiotic, a pharmaceutically acceptable chelating agent and a pharmaceutically acceptable pH buffering agent (Fig. 1). Another aspect of the present invention is a medical dressing for delivering an antimicrobial composition to a site of a skin injury or lesion of a mammal, comprising a support and an antimicrobial agent and at least one chelating agent. The present invention also relates to methods for delivering an antibiotic to an injury to the skin of a human o animal and to kits for the preparation and use of an antimicrobial comosition to inhibit a microbial infection of a skin injury or lesion of a human or animal.