Broad-spectrum antibiotic

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.^[3]

Uses

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.

Risks

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^[4]. 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^[5] (also known as "C. diff") or Candidiasis (also known as "thrush") in females. This side-effect is more likely with the use of broad-spectrum antibiotics^[6].

Examples

In medicine:

• amoxicillin
• imipenem
• levofloxacin, gatifloxacin, moxifloxacin

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

Others:

• streptomycin
• tetracycline
• chloramphenicol

Slightly-Broad:

• ampicillin

See also

• Empiric therapy

References

• Clayton L. Thomas Editor, Taber's Cyclopedic Medical Dictionary 17th ed., 1993 (ISBN 0-8036-8313-8)
• S.J. Hopkins, Drugs and Pharmacology for Nurses 12th ed., 1997 (ISBN 0-443-05249 2)
• Ibid
• E.A. Martin, Oxford Concise Medical Dictionary 6th ed., 2003 (ISBN 0-19-860753-9)