Antibiotics were first discovered in the late 1920s but were not routinely used clinically until the early 1940s during the Second World War. They can be used as an adjunct to endodontic treatment in a number of ways-systemically, prophylactically and locally. There are few real indications for the systemic use of antibiotics in conjunction with endodontic treatment. They are only needed when the body's efforts at fighting bacteria are failing. Use of antibiotics to prevent infection (antibiotic prophylaxis) may prevent some case of bacterial endocarditis. Therefore, prophylaxis is recommended for individuals in high-risk and moderate-risk categories. Another mode of application of antibiotics is local application as intracanal medicaments and root canal irrigants.