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What are Broad-Spectrum Antibiotics?

Mary McMahon
Updated May 17, 2024
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Broad-spectrum antibiotics are antibiotics which are designed to work against a broad spectrum of bacteria, rather than narrow-spectrum antibiotics, which are only effective against a smaller range of bacteria. These medications are classically used in cases in which a doctor is not sure about the identity of a disease-causing organism and wants to provide a patient with medication which will rapidly attack the infection, rather than waiting for culture results and prescribing a narrow-spectrum antibiotic which is more targeted in effect.

Some examples of broad-spectrum antibiotics include penicillin, cephalosporin, tetracycline, ciprofloxacin, and levofloxacin. These drugs work on both gram-negative and gram-positive organisms. When a patient appears to have a bacterial infection, a broad-spectrum antibiotic is the most likely to provide effective treatment without knowing which organism is behind the infection. For example, when a patient comes to a doctor with bronchitis, the doctor may prescribe a general antibiotic medication to treat the infection without taking a culture.

If an infection persists or it appears unusual in nature, cultures will be done. In a culture, a sample of the bacteria is collected and grown to find out which organism is responsible for the infection. Furthermore, a culture can also be used to test antibiotics in case an organism is antibiotic-resistant. In this case, the culture is used to find the drug which will be most effective so that the patient does not have to try several unsuccessful antibiotics before finding one which works.

One problem with broad-spectrum antibiotics which began to grow in the late 20th century was the emergence of antibiotic resistance in bacteria. Almost as soon as humans started developing antibiotics, bacteria started swapping genes which they could use to survive antibiotic therapy. In some cases, organisms developed resistance to multiple antibiotics, making treatment of infections involving these organisms very challenging. More advanced classes of antibiotics were developed in response, but bacteria also adapted to address these. A broad-spectrum antibiotic is only useful as long as it kills most bacteria and organisms which can quickly adapt to resist antibiotics present a significant challenge.

Concerns about resistance to antibiotics have led to some recommendations that doctors change the way they use and prescribe these medications. Doctors are encouraged to only prescribe a broad-spectrum antibiotic when a patient cannot fight an infection off on his or her own, for example. In addition, patients are instructed in the importance of completing a course of antibiotics fully in order to avoid promoting the development of antibiotic resistance.

WiseGeek is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a WiseGeek researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By Idova77 — On Apr 11, 2011

@anon144463 - I agree. This definitely helps to explain why it is dangerous to use broad-spectrum antibiotics without medical supervision.

Some people use antibiotics that were previously prescribed for another infection. Some people get broad-spectrum antibiotics from Canada or Mexico without a prescription and self medicate without adequate information.

The final result is that new strains of antibiotic resistant bacteria develop and thrive from the misuse and overuse of these meds. Then, when you really need the medicine to kill the bacteria, it won't work.

The bacteria has made itself stronger than the antibiotic because it had the opportunity to become familiar with the potency of the medicine (so to speak).

By anon144463 — On Jan 19, 2011

good information! this helps.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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