Ceftazidime Does NOT Provide Anaerobic Coverage
Ceftazidime has no anaerobic activity and requires the addition of metronidazole for infections involving anaerobic organisms. 1
Spectrum Limitations
Ceftazidime lacks activity against anaerobes, including Bacteroides fragilis, which is a critical pathogen in intra-abdominal and polymicrobial infections 1, 2
The FDA label explicitly states that while ceftazidime has activity against many Bacteroides species, "many isolates of Bacteroides species are resistant" 2
Multiple research studies from the 1980s confirm ceftazidime has "limited activity against gram-negative anaerobes" 3, 4
Clinical Implications
For intra-abdominal infections or any polymicrobial infection with suspected anaerobic involvement, ceftazidime MUST be combined with metronidazole 1
This is a common pitfall: using ceftazidime for intra-abdominal infections without adding metronidazole for anaerobic coverage 1
Contrast with Piperacillin-Tazobactam
Unlike ceftazidime, piperacillin-tazobactam provides comprehensive anaerobic coverage as monotherapy, eliminating the need for additional metronidazole 5
Piperacillin-tazobactam has a "broad anaerobic spectrum" and is recommended as single-agent therapy for intra-abdominal infections 5
Novel β-lactam/β-lactamase inhibitor combinations such as ceftazidime-avibactam also lack intrinsic anaerobic activity and require metronidazole, similar to ceftazidime alone 5
What Ceftazidime DOES Cover
Ceftazidime excels at gram-negative coverage, particularly Pseudomonas aeruginosa, which is its primary clinical niche 6, 3, 4
It has activity against Enterobacteriaceae and is stable against many beta-lactamases 3
However, it has poor activity against gram-positive cocci (including staphylococci and streptococci) and no activity against anaerobes 1, 3