When treating any infectious disease, a physician selects an antimicrobial based on the following considerations: the in vitro activity of the drug, its pharmacokinetic properties, the efficacy data based on properly designed and conducted clinical trials, and finally the adverse effects. In this article, all of these factors, with the exception of adverse effects, were discussed. It was neither my intent nor my purpose to deal with side effects or adverse drug reactions because these are well covered in standard texts or physician references such as the Physicians' Desk Reference and the American Hospital Formulary Service (United States) and the Compendium of Pharmaceuticals and Specialties (Canada).