Clinical Cases

• Case 1 – Community-acquired perforated appendicitis (appropriate cefoxitin use)

  • Clinical scenario

    • A 24-year-old otherwise healthy man presents with 24 hours of abdominal pain migrating to the RLQ, fever 38.9°C, leukocytosis 17,000/µL.

    • CT abdomen shows perforated appendicitis with localized fluid.

    • Patient undergoes urgent laparoscopic appendectomy with localized peritonitis.

      • Empiric postoperative antibiotics: Cefoxitin 2 g IV q6 h.

      • Cultures from peritoneal fluid grow pan-susceptible E. coli and Bacteroides fragilis.

        • The patient defervesces within 48 hours and completes 4 days of IV cefoxitin followed by 3 days of oral amoxicillin-clavulanate.

      • Patient  recovers uneventfully.

  • Teaching Points

    • This is mild–moderate community-acquired complicated intra-abdominal infection with typical flora and low suspicion for ESBL/AmpC producers.

    • SIS/IDSA guidelines specifically allow cefoxitin monotherapy in such mild–moderate community-acquired intra-abdominal infection when local resistance is favorable.^2,3 

    • The presence of B. fragilis underscores the value of cefoxitin’s strong anaerobic activity.⁴

• Case 2 – Pelvic inflammatory disease (PID) with tubo-ovarian abscess

  • Clinical scenario

    • A 29-year-old woman presents with 3 days of pelvic pain, fever 39.1°C, cervical motion tenderness, and a tender adnexal mass on exam. Transvaginal ultrasound shows a 4-cm tubo-ovarian abscess. Pregnancy test is negative.

    • She is admitted and started on cefoxitin 2 g IV q6 h + doxycycline 100 mg IV q12 h + metronidazole 500 mg IV q12 h.

    • Over 48–72 hours, she improves clinically; the abscess size decreases on repeat imaging without need for drainage. She is discharged to complete a 14-day course of oral doxycycline and metronidazole.

  • Teaching points

    • CDC/StatPearls recommend parenteral cefoxitin-based regimens as one of the inpatient treatment options for PID.^5,6,7

    • Cefoxitin provides excellent anaerobic and Enterobacterales coverage in the pelvis, while doxycycline addresses Chlamydia and atypicals.

      • Metronidazole further reinforces anaerobic coverage.

    • Clinical improvement and radiologic downsizing of the abscess support adequate anaerobic and polymicrobial coverage without immediate need for drainage.

• Case 3 – Biliary sepsis with AmpC-producing Enterobacter cloacae (cefoxitin failure)

  • Clinical scenario

    • A 70-year-old man with diabetes and prior hospitalizations presents with fever, jaundice, and RUQ (Right Upper Quadrant) pain.

      • Imaging shows acute calculous cholecystitis with suspected common bile duct obstruction.

      • He undergoes urgent ERCP and biliary drainage.

    • Empiric antibiotics started in the ED: cefoxitin 2 g IV q6 h for presumed polymicrobial intra-abdominal infection.

    • Blood cultures later grow Enterobacter cloacae complex; susceptibility panel initially reports cefoxitin “susceptible.”

      • After 48 hours, the patient remains febrile and hypotensive.

      • Infectious diseases is consulted and notes that Enterobacter cloacae is an inducible AmpC producer; therapy is switched to cefepime.

      • Within 24–48 hours of cefepime, the patient’s clinical status improves.

  • Teaching points^9,10

    • Cephamycins (cefoxitin) are poor choices for serious infections caused by organisms at high risk of inducible AmpC expression (e.g., Enterobacter cloacae).

    • EUCAST expert rules and the 2024 IDSA AMR guidance specifically address this issue: laboratory “susceptibility” does not guarantee clinical success when an inducible AmpC is present.

    • This case illustrates why clinical evaluation must consider underlying resistance mechanisms, not just categorical S/I/R calls.

      • S/I/Rs calls: 

        • "S/I/R calls" (or SIR) usually refers to Susceptibility Interpretation Results in microbiology, which classify how bacteria respond to antibiotics": 

          • S (Sensitive): The infection is likely to respond to the antibiotic.

          • I (Intermediate): The antibiotic may work, but it is less reliable.

          • R (Resistant): The antibiotic will not kill the bacteria.⁸