## **Core Concept**
Third-generation cephalosporins are a class of β-lactam antibiotics characterized by their broad spectrum of activity, particularly against Gram-negative bacteria. They are often used to treat severe infections, including meningitis, pneumonia, and sepsis. These antibiotics have a different side chain that allows them to bind to penicillin-binding proteins (PBPs) in Gram-negative bacteria more effectively.

## **Why the Correct Answer is Right**
Ceftriaxone is a third-generation cephalosporin with a broad spectrum of activity against both Gram-positive and Gram-negative bacteria. It is commonly used for treating infections such as meningitis and pneumonia.

## **Why Each Wrong Option is Incorrect**
* **Option A:** Cefotaxime is a third-generation cephalosporin. It has a broad spectrum of activity and is used to treat a variety of infections, including urinary tract infections and respiratory tract infections.
* **Option B:** Ceftazidime is also a third-generation cephalosporin with potent activity against Pseudomonas aeruginosa, in addition to other Gram-negative bacteria.
* **Option D:** Cefepime is a fourth-generation cephalosporin. It has an even broader spectrum of activity than third-generation cephalosporins, including activity against beta-lactamase-producing strains of bacteria.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is the classification and spectrum of activity of cephalosporins. Third-generation cephalosporins have a broad spectrum of activity but generally do not cover Pseudomonas aeruginosa as well as fourth-generation cephalosporins like cefepime.

## **Correct Answer:** D. Cefepime