Because many antibiotics are excreted into the breast milk, it can be difficult for a practitioner to choose an antibiotic for a lactating patient that will have minimal risks to her nursing infant. This article is the last of a three-part series discussing the use of anti-infective agents during lactation. The authors review general information with regard to use and common side effects for several classes of antibiotics. They summarize information, including available safety data, documented milk concentrations, milk-to-plasma ratios, and other pharmacokinetic properties, to help practitioners choose antibiotics that may be considered safe to use in the lactating mother.