Start with severity
A dog comes in with bloody diarrhoea. He's quiet, tachycardic and dehydrated. Would you start antibiotics?
Blood in the stool alone is not an indication. The dog's general condition, response to fluids and relevant CBC findings determine whether systemic antimicrobials should be considered.
A dog in shock or with marked circulatory compromise or organ dysfunction needs immediate assessment and stabilization. Do not wait for bloodwork or a fluid trial. Suspected parvovirus, obstruction, significant immunocompromise or another specific disease needs a separate diagnostic pathway. So do persistent or recurrent episodes.
| Clinical presentation | Antimicrobial decision |
|---|---|
| Mild. Bright and responsive, with no dehydration, hypovolaemia or systemic illness. | No routine antibiotics, even if the stool contains blood. Supportive outpatient care is generally appropriate. |
| Moderate. Reduced general condition with dehydration or hypovolaemia. Any systemic signs attributable to fluid deficits improve after adequate fluid replacement. | No routine antibiotics if the dog responds to fluids and has no qualifying inflammatory CBC findings. Continue supportive care and reassess. |
| Severe. Critical illness at presentation, or systemic signs that persist, worsen or recur despite adequate fluid replacement. | Consider systemic antimicrobials alongside urgent stabilization, further investigation and supportive care. |
ENOVAT makes a strong recommendation against routine antimicrobials in mild and moderate disease. Its suggestion to use them in severe disease is conditional because the evidence is more limited.
If the dog is moderately unwell
Two checks can change the antimicrobial decision.
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Reassess after fluid replacement.
Have mental status, perfusion and other systemic findings improved with appropriate fluids? If signs persist or recur despite adequate replacement, reassess the dog as severe disease. If the response has not been assessed yet, the antimicrobial decision is still pending unless qualifying CBC findings independently support systemic treatment.
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Review the CBC.
ENOVAT advises a complete blood count (CBC) and biochemistry for moderate or severe presentations. In a dog with moderate disease, the following findings are exceptions to the usual recommendation against antimicrobials:
- Absolute neutrophil count >25 × 10⁹/L (more than 25,000/µL).
- Neutropenia relative to the laboratory's reference interval.
- A confirmed degenerative left shift.
Interpret the findings in the patient's clinical context. If the CBC is unavailable, severe inflammatory changes have not been excluded. Dehydration alone does not establish an antimicrobial indication.
Why routine antibiotics are discouraged
Across six randomised trials involving 232 dogs with mild or moderate acute diarrhoea, the pooled estimate was 0.28 days less diarrhoea with antimicrobials, around seven hours. The ENOVAT panel considered a reduction of less than one day clinically trivial. Dogs with severe disease were not included in those trials.
Assess the current patient
Acute Diarrhoea Triage lets you enter severity, response to fluids and clinician-interpreted CBC findings. It shows the resulting antimicrobial pathway and estimates the fluid deficit when weight and dehydration are entered. The deficit estimate is not a complete fluid plan.
A dog with bloody diarrhoea: worked example
A dog has had bloody diarrhoea for 24 hours. He's quiet, tachycardic and dehydrated, without signs of shock or organ dysfunction. After appropriate fluid replacement, his attitude and perfusion improve. His CBC shows none of the qualifying inflammatory findings above.
Assessment: Moderate disease. Continue supportive care and monitoring. Routine antimicrobials are not recommended.
If systemic signs persist or return despite adequate fluids, the dog needs prompt reassessment for severe disease. A qualifying CBC finding also changes the antimicrobial assessment. If parvovirus, obstruction or another specific illness is suspected, investigate that separately.
When systemic antimicrobials are considered
Stabilization and diagnostic assessment remain priorities. Consider appropriate sampling and culture when bacteraemia or sepsis is suspected, without delaying urgent treatment.
ENOVAT describes narrower parenteral first-line options for severe disease without critical illness or major resistance concerns. Critical illness, likely resistance, or failure of appropriate first-line antimicrobials together with supportive care may call for broader coverage. The regimen needs a patient and product review, including renal function, perfusion and local antimicrobial guidance where relevant.
Review antimicrobial treatment daily in hospitalized dogs and stop when clinically resolved. The ENOVAT discussion of a typical 3 to 7 day treatment period is context, not a fixed course for every patient.
Open Acute Diarrhoea Triage
For the next case, record the clinical findings, review the recommendation and check any remaining safety steps before using calculated treatment options in Vetool.
Reference
- ENOVAT guidelines on antimicrobial use in canine acute diarrhoea (2024).
For veterinary professionals
Assess each patient individually and follow current references, local antimicrobial policies and product information. Urgent care should never wait for completion of a digital tool.