What is meant by the term 'narrow-spectrum antibiotic agent'?

What is meant by the term 'narrow-spectrum antibiotic agent'?

• A. An antimicrobial that is effective only against bacteria
• B. An antimicrobial that has a narrow therapeutic index
• C. An antimicrobial that can only be given in very small doses because of toxicity concerns
• D. An antimicrobial that is mainly effective against a few Gram-positive or Gram-negative bacteria

Answer: (D)

Narrow-spectrum antibiotics are defined by the limited range of bacteria they affect. They target a small, specific group of organisms—often mainly Gram-positive or mainly Gram-negative bacteria—rather than acting on a wide variety of bacteria. This focused effectiveness is why the correct choice describes an agent that is mainly active against a few Gram-positive or Gram-negative bacteria. Using such an antibiotic when the causative organism is known helps preserve normal flora and reduce broader resistance. The other ideas don’t fit this concept: spectrum is about the breadth of bacteria targeted, not safety margins or dosing limits, and stating “effective only against bacteria” doesn’t specify the limited range within bacteria.

Narrow-spectrum antibiotics are defined by the limited range of bacteria they affect. They target a small, specific group of organisms—often mainly Gram-positive or mainly Gram-negative bacteria—rather than acting on a wide variety of bacteria. This focused effectiveness is why the correct choice describes an agent that is mainly active against a few Gram-positive or Gram-negative bacteria. Using such an antibiotic when the causative organism is known helps preserve normal flora and reduce broader resistance. The other ideas don’t fit this concept: spectrum is about the breadth of bacteria targeted, not safety margins or dosing limits, and stating “effective only against bacteria” doesn’t specify the limited range within bacteria.