There is a common misconception that resistance will emerge if a prescribed antibiotic course is not completed. Premature cessation of antibiotic therapy will not increase the risk that resistance will emerge. For most infections, the recommended duration of therapy (5–14 days, depending on syndrome) is based on expert opinion and convention, rather than solid evidence. However, for many syndromes associated with bacteraemia, there is no difference in outcome when shorter courses are used. In practice the optimal duration of therapy depends on clinical syndrome, the causative organism, whether source control is possible and the patient's response to therapy. For example, only 3–5 days of treatment is needed for meningococcal meningitis, compared with 10–14 days for pneumococcal meningitis. Additional studies are needed to validate shorter courses of antibiotic therapy for many other infections.
Resistance is much more likely to occur with long antibiotic courses, which are rarely indicated except when the site of infection is relatively inaccessible (in biofilm in sites such as a cardiac valve or foreign body or in an abscess); these infections often cannot be cured without surgical removal of the source or drainage of pus. There is no risk — and every advantage — in stopping a course of an antibiotic immediately a bacterial infection has been excluded or is unlikely; and minimal risk if signs and symptoms of a mild infection have resolved.