Background: Antibiotics generally are recommended to treat hemorrhagic gastroenteritis (HGE). Inappropriate use of antibiotics may promote risk of antimicrobial resistance and unnecessary adverse drug reactions. The necessity of antimicrobial therapy in dogs with HGE has not been demonstrated. Objective: The purpose of this prospective, placebo‐controlled, blinded study was to evaluate whether treatment with amoxicillin/clavulanic acid improves the clinical course and outcome of HGE in dogs that show no signs of sepsis. Animals: The study included 60 dogs diagnosed with HGE between 2007 and 2009 at the Clinic of Small Animal Medicine, LMU University of Munich, Germany. The inclusion criterion was the presence of acute hemorrhagic diarrhea (<3 days). Dogs pretreated with antibiotics, with signs of sepsis, or diagnosed with any disease known to cause bloody diarrhea were excluded from the study. Methods: Patients were randomly divided into treatment (amoxicillin/clavulanic acid for 7 days) and placebo groups. To evaluate treatment efficacy, severity of clinical signs (based on a newly developed HGE index), duration of hospitalization, and mortality rate were compared between the 2 groups. Results: Fifty‐three of 60 dogs completed the study. No significant difference between treatment groups concerning mortality rate, dropout rate, duration of hospitalization, or severity of clinical signs, either on any individual day or over the course of disease, was observed. Conclusions and Clinical Importance: In some dogs with HGE that show no signs of sepsis, antibiotics may not change the case outcome or time to recovery.

No prospective studies including large numbers of dogs with acute haemorrhagic diarrhoea syndrome (AHDS) are published so far. The aim of this case-control study was to describe signalment, history, clinical signs, laboratory values and course of disease in dogs with AHDS. Dogs (108) with idiopathic acute haemorrhagic diarrhoea (<3 days) were prospectively enrolled. Clinical assessment was performed by calculation of the 'AHDS index' (0-18). The hospital population and 21 healthy dogs served as control groups. Dogs with AHDS had a significantly lower body weight (median 9.8 kg) and age (median five years) than other dogs of the hospital population (20 kg; 10 years) (P<0.001). Predisposed breeds were Yorkshire terrier, miniature pinscher, miniature schnauzer and Maltese. The syndrome was more likely to occur during winter. Vomiting preceded the onset of bloody diarrhoea in 80 per cent of dogs and haematemesis was observed in half of those cases. Median AHDS index at presentation was 12 (range 3-17). Haematocrit was generally high (median 57.1 per cent; range 33-76 per cent), but exceeded 60 per cent only in 31.4 per cent of dogs. Haematocrit of 48.1 per cent of dogs was above reference range, as was monocyte (50.0 per cent), segmented (59.6 per cent) and band neutrophil count (45.2 per cent). A rapid clinical improvement occurred during the first 48 hours.

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