Sepsis in dogs: antibiotic de-escalation after culture
7-year-old crossbreed bitch operated on for septic peritonitis after enterotomy dehiscence. She is receiving intravenous ampicillin and marbofloxacin. At 72 hours she is stable and eating, and abdominal fluid culture grows Escherichia coli susceptible to amoxicillin-clavulanate and cefalexin.
What do you do with the antibiotic treatment?
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A. Keep both antibiotics for at least 4 weeks to ensure cure
With surgical source control there is no justification for such long courses or for keeping two drugs, and they increase adverse effects and selection of resistance.
B. Add a carbapenem to cover possible unisolated bacteria
Carbapenems are critically important antimicrobials in human medicine (EMA category A) and are not justified in a patient who is improving with an organism susceptible to first-line drugs.
C. Stop all antibiotics, because surgery has already resolved the source
Source control is essential, but the peritoneal infection remains active for a few days; stopping abruptly at 72 hours without resolution criteria is premature.
D. De-escalate: stop the fluoroquinolone and continue with a narrower-spectrum beta-lactam to which the organism is susceptible, switch to oral when tolerated and tailor duration to progress
Correct. Empirical broad-spectrum therapy is justified at the start because delay kills, but it is provisional: with culture results and clinical improvement the spectrum is narrowed, reducing toxicity, cost and resistance.
lightbulb Key takeaway
In sepsis: cultures before antibiotics, intravenous broad-spectrum antibiotics as soon as possible, source control and reassessment at 48–72 hours to de-escalate. Fluoroquinolones are EMA category B: use them only when susceptibility testing justifies it.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.