Cephalosporins are a large and varied class of antibiotics that is conceptually split into five different "generations." As the generations progress, so do their gram-negative coverages.

First Generation

The 1st generation has a fair amount of gram-positive coverage (including S. aureus) with very basic gram-negative coverage. This is why 1st generation cephalosporins are often used for surgical prophylaxis to prevent skin/surgical site infections.

Cefazolin (Ancef)
Cefalexin (Keflex)

Second Generation

The 2nd generation has less gram-positive coverage than the 1st generation, but has better gram-negative coverage.

Third Generation

The 3rd generation has more gram-negative coverage than the 2nd generation, but less gram-positive coverage. Ceftazidime stands out as the only 3rd generation cephalosporin with antipseudomonal coverage.

Ceftriaxone (Rocephin)
Cefdinir (Omnicef)
Cefpodoxime (Vantin)
Cefixime
Cefotaxime
Ceftazidime Antipseudomonal

Fourth Generation

The 4th generation, while small, has good pseudomonal spp coverage (hence why many patients are started on a 4th generation cephalosporin, then de-escalated once pseudomonas is ruled out).

Cefepime

Fifth Generation

The 5th generation has the same gram-negative coverage as the 3rd and 4th generations, but has significantly better gram-positive coverage, including MSSA, MRSA and S. pneumoniae, and is considered to be a very broad-spectrum.