Antibiotics in Acute Diarrhea (ENOVAT guidelines)

The use of antibiotics in dogs with acute diarrhea is a widely discussed topic in veterinary practice. Most cases of diarrhea are self-limiting and resolve with supportive care. Unnecessary antimicrobial use contributes to antimicrobial resistance and can significantly disrupt the intestinal microbiome. The European Network for Optimization of Veterinary Antimicrobial Therapy (ENOVAT), in collaboration with the World Small Animal Veterinary Association (WSAVA), has developed evidence-based guidelines to support veterinarians in responsible antibiotic use in dogs with acute diarrhea.

These guidelines divide the patients in different groups, based on the severity of their clinical disease:

Group 1: Mild acute, non-hemorrhagic diarrhea

• Dogs in good general condition, without signs of dehydration or systemic illness*.
• Recommendation: No antibiotics.

Group 2: Mild acute hemorrhagic diarrhea

• Dogs with bloody diarrhea but in otherwise good general condition, without signs of dehydration or systemic illness.
• Recommendation: No antibiotics.

Group 3: Moderate acute, non-hemorrhagic diarrhea

• Dogs that are generally ill and show signs of dehydration/hypovolemia and/or systemic illness, BUT that fully recover with fluid therapy.*
• Recommendation: No antibiotics.

Group 4: Moderate acute hemorrhagic diarrhea

• Dogs with hemorrhagic diarrhea that are generally ill and showing signs of dehydration/hypovolemia and/or systemic illness, BUT that fully recover with fluid therapy.*
• Recommendation: No antibiotics.
• Exception: If there is evidence of severe/systemic inflammation (marked neutrophilia >25×10^9/L, neutropenia, or degenerative left shift**), antibiotics should be considered.

Group 5: Severe disease (non-hemorrhagic and hemorrhagic diarrhea)

• Dogs with persistent signs of systemic illness* despite adequate fluid therapy.
• Recommendation: Systemic antibiotics are advised.
• Antibiotic choice depends on how critically ill the animal is, regional prevalence of antimicrobial resistance and drug availability:
  • Non-critical illness: ampicillin (or amoxicillin-clavulanate) or trimethoprim-sulfonamides as first line drugs.
  • Critical illness or where resistant bacteria are more likely: four-quadrant coverage (covering Gram-negatives, Gram-positives, anaerobes, and aerobes) using aminopenicillin or clindamycin combined with a fluoroquinolone or aminoglycoside (gentamicin, amikacin)***.
• Treatment duration depends on clinical response and should be re-evaluated daily:
  • Treat until clinical recovery.
  • Usually 3–7 days.

The guidelines do not provide a clear recommendation for or against the use of probiotics in dogs with acute diarrhea.

*Systemic illness or SIRS criteria in dogs:

1. Hypo- or hyperthermia
2. Tachycardia (heart rate >120/min)
3. Tachypnea (respiratory rate >20/min)
4. Neutrophilia (>16×10^9/L) or neutropenia (<1×10^9/L)

Degenerative left shift = the presence of a left shift (band neutrophils) where there are more immature band neutrophils than mature segmented neutrophils.

***Potential side effects: fluoroquinolones in young, growing animals may cause cartilage damage. Aminoglycosides may cause ototoxicity and nephrotoxicity.

Conclusion

Antibiotics should only be used when there is a clear indication of systemic infection and never routinely in uncomplicated acute diarrhea.