For colorectal procedures, which antibiotic combination is typical for prophylaxis?

• A. Vancomycin alone
• B. Amoxicillin-clavulanate
• C. Ciprofloxacin alone
• D. Cefazolin with metronidazole

Answer: (D)

Prophylaxis for colorectal surgery aims to cover organisms from skin and from the colon. The colon harbors anaerobes like Bacteroides and facultative gram-negative bacteria such as E. coli, so an effective prophylactic regimen must address both groups to prevent surgical-site and intra-abdominal infections.

Cefazolin provides good protection against common skin flora and some gram-negative rods, while metronidazole targets anaerobic bacteria. Together, they offer broad coverage of the typical flora encountered during colorectal procedures without overly broad or unnecessary spectrum. This combination is preferred because it reliably reduces infectious complications in this setting and is practical in terms of safety and cost.

Other options either miss anaerobic coverage (vancomycin alone, ciprofloxacin alone) or do not provide the same reliable anaerobic coverage alongside skin and enteric flora (amoxicillin-clavulanate can cover anaerobes but is not the standard first-line choice for colorectal prophylaxis in many guidelines).