A broad-spectrum antibiotic is so called due to its activity against a wide range of infectious agents. A good example is amoxicillin.

Uses

Broad-spectrum antibiotics are used in roughly two medical situations:

• Where the infectious agent will not become known in the course of the disease, e.g. in a child moderately ill with bronchitis. In this case no cultures are being taken.
• When the patient is ill enough to warrant antibiotic treatment, even though culture results are not yet known. This occurs, for example, in meningitis, where the patient is so ill that he/she would die within hours if broad-spectrum antibiotics are not initiated.

Generally, the spectrum is "narrowed down" when the causative agent of an infection becomes known, and the broad-spectrum agent is replaced by a narrower-spectrum antibiotic. This is supposed to limit the development of antibiotic resistance, although evidence for this practice is unclear.