Broad-spectrum antibiotic

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The term broad-spectrum antibiotic refers to an antibiotic that acts against a wide range of disease-causing bacteria.[1] A broad-spectrum antibiotic acts against both Gram-positive and Gram-negative bacteria, in contrast to a narrow-spectrum antibiotic, which is effective against specific families of bacteria.[2] An example of a commonly used broad-spectrum antibiotic is ampicillin.[2]


Broad-spectrum antibiotics are properly used in the following medical situations:

  • Empirically (i.e., based on the experience of the practitioner), prior to the formal identification of the causative bacteria, when there is a wide range of possible illnesses and a potentially serious illness would result if treatment is delayed. This occurs, for example, in meningitis, where the patient can become fatally ill within hours if broad-spectrum antibiotics are not initiated.
  • For drug resistant bacteria that do not respond to other, more narrow-spectrum antibiotics.
  • In the case of superinfections, where there are multiple types of bacteria causing illness, thus warranting either a broad-spectrum antibiotic or combination antibiotic therapy.
  • For prophylaxis within one hour before incision, for an operation, in order to prevent bacterial infections occurring.


As a side-effect, antibiotics can change the body's normal microbial content by attacking indiscriminately both the pathological and naturally occurring, beneficial or harmless bacteria found in the intestines, lungs and bladder.[3] The destruction of the body's normal bacterial flora provides an opportunity for drug-resistant microorganisms to grow vigorously and can lead to a secondary infection such as Clostridium difficile[2] (also known as "C. diff") or Candidiasis (also known as "thrush"). This side-effect is more likely with the use of broad-spectrum antibiotics.[3]


In humans:

In veterinary medicine, co-amoxiclav, (in small animals); penicillin & streptomycin and oxytetracycline (in farm animals); penicillin and potentiated sulfonamides (in horses).

See also[edit]


  1. ^ Clayton L. Thomas, ed. (1993). Taber's Cyclopedic Medical Dictionary (17th ed.). F. A. Davis Co. ISBN 0-8036-8313-8. 
  2. ^ a b c S. J. Hopkins (1997). Drugs and Pharmacology for Nurses (12th ed.). Churchill Livingstone. ISBN 0-443-05249-2. 
  3. ^ a b E. A. Martin (2003). Oxford Concise Medical Dictionary (6th ed.). Oxford University Press. ISBN 0-19-860753-9.