Gram-negative coverage — Which listed antimicrobial agent has poor activity against Enterobacteriaceae and therefore is generally not used to treat their infections?

Introduction / Context:
Enterobacteriaceae are aerobic Gram-negative bacilli (e.g., E. coli, Klebsiella). Appropriate empiric therapy requires agents with reliable Gram-negative activity. Clindamycin is primarily active against Gram-positive cocci and anaerobes and is ineffective against Enterobacteriaceae.

Given Data / Assumptions:

• Clindamycin: lincosamide; Gram-positive and anaerobic coverage; poor Gram-negative aerobic activity.
• Cefoxitin: second-generation cephalosporin with some Enterobacteriaceae coverage and anaerobic activity.
• Trimethoprim-sulphamethoxazole: active against many Enterobacteriaceae (local resistance varies).
• Ciprofloxacin: potent Gram-negative activity including Enterobacteriaceae.

Concept / Approach:
Exclude drugs with recognized Enterobacteriaceae activity; identify the outlier with poor Gram-negative aerobic coverage: clindamycin.

Step-by-Step Solution:

Verification / Alternative check:
Institutional antibiograms and standard references consistently show negligible Enterobacteriaceae susceptibility to clindamycin.

Why Other Options Are Wrong:

• Cefoxitin: covers several Enterobacteriaceae (though resistance patterns vary).
• Trimethoprim-sulphamethoxazole: commonly used for UTIs caused by Enterobacteriaceae.
• Ciprofloxacin: strong Gram-negative coverage.

Common Pitfalls:
Overgeneralizing clindamycin’s good anaerobic activity to Gram-negative aerobes; it does not extend to Enterobacteriaceae.

Final Answer:
clindamycin