Ceftazidime is a third‑generation cephalosporin that primarily covers aerobic Gram‑negative bacteria, including Pseudomonas aeruginosa, with minimal Gram‑positive and no meaningful anaerobic activity.

Core coverage (“what it covers”)

  • Strong Gram‑negative coverage: Enterobacterales such as E. coli, Klebsiella, Proteus, Enterobacter, Serratia, Citrobacter, and others, including many beta‑lactamase–producing strains.
  • Key anti‑pseudomonal agent: Reliable activity against Pseudomonas aeruginosa is its main distinguishing feature among third‑generation cephalosporins.
  • Very limited Gram‑positive activity: Poor for staphylococci and streptococci, so it is not chosen when robust Gram‑positive coverage is needed.
  • No meaningful anaerobic coverage: Does not adequately treat Bacteroides or other anaerobes and must be combined with another agent (for example, metronidazole) if anaerobes are a concern.

Typical clinical uses

  • Hospital‑acquired and ventilator‑associated pneumonia when Pseudomonas is suspected or documented.
  • Serious Gram‑negative infections such as bacteremia, complicated urinary tract infections, and some intra‑abdominal or biliary infections, usually as part of combination therapy if anaerobes or Gram‑positives are also likely.
  • Empiric or targeted therapy in high‑risk settings (for example, neutropenic fever) when strong Gram‑negative and anti‑pseudomonal activity is needed, though some guidelines now favor agents with better Gram‑positive coverage like cefepime.

Important non‑coverage (“what it does not cover”)

  • No Enterococcus and weak staphylococcal coverage: Other agents are required when Enterococcus, MRSA, or serious MSSA are suspected.
  • No reliable anaerobes: Not appropriate alone for mixed intra‑abdominal or pelvic infections where anaerobes are common.
  • Does not address many multidrug‑resistant organisms (for example, carbapenem‑resistant strains) unless combined with a beta‑lactamase inhibitor such as avibactam in the ceftazidime‑avibactam product.

Quick comparison point

  • Compared with ceftriaxone: ceftazidime has better Gram‑negative and Pseudomonas activity but worse Gram‑positive and anaerobic coverage.
  • In practice, it is reserved for situations where suspected or proven Pseudomonas justifies its focused, Gram‑negative–heavy spectrum to help limit resistance from overuse of broad‑spectrum drugs.

Bottom line: ceftazidime is mainly a Gram‑negative, especially anti‑pseudomonal, drug with little Gram‑positive and no anaerobic coverage, best used when those specific pathogens are the main concern.