## Core Concept
Third-generation cephalosporins are a class of β-lactam antibiotics that have a broad spectrum of activity, particularly against Gram-negative bacteria. They are characterized by their ability to cross the blood-brain barrier and are often used to treat severe infections. These antibiotics work by inhibiting bacterial cell wall synthesis.

## Why the Correct Answer is Right
Ceftriaxone, ceftazidime, and cefotaxime are well-known third-generation cephalosporins. They have extended activity against Gram-negative bacteria compared to first and second-generation cephalosporins. Cefepime is actually considered a fourth-generation cephalosporin due to its broader spectrum of activity, including increased resistance to β-lactamases and activity against certain Gram-positive bacteria.

## Why Each Wrong Option is Incorrect
* **Option A: Ceftriaxone** - This is a third-generation cephalosporin with a broad spectrum of activity, particularly noted for its use in treating meningitis and pneumonia.
* **Option B: Ceftazidime** - This is also a third-generation cephalosporin, known for its potent activity against Pseudomonas aeruginosa, among other Gram-negative bacteria.
* **Option C: Cefotaxime** - Another third-generation cephalosporin, often used for similar indications as ceftriaxone and ceftazidime.

## Why Option D is Correct
* **Option D: Cefepime** - This is a fourth-generation cephalosporin. It has a broader spectrum of activity than third-generation cephalosporins, including more Gram-positive coverage and retained activity against Gram-negative bacteria.

## Clinical Pearl / High-Yield Fact
A key point to remember is the distinction between third and fourth-generation cephalosporins, particularly in terms of their spectra of activity and uses in clinical practice. For example, cefepime's activity against certain Gram-positive cocci and its use in febrile neutropenia make it stand out.

## Correct Answer: D. Cefepime.