We all know that inappropriate use of antibiotics in veterinary medicine is being ferreted out more and more since antimicrobial resistance is on the rise. Furthermore, inappropriate use of antibiotics can disrupt normal, protective intestinal flora and raise the risk for bacterial translocation and sepsis.

Idiopathic hemorrhagic gastroenteritis (HGE), one cause of acute hemorrhagic diarrhea in dogs, is often treated with antibiotics. However, the necessity for antimicrobial therapy has not been determined. Theories of bacterial translocation, bacterial causes, and the potential for sepsis have led to widespread use of antibiotics in dogs presenting with acute hemorrhagic diarrhea.

Amoxicillin/clavulanic acid, a commonly used antibiotic because of its broad spectrum and safety, is often a first-line choice in cases of HGE. A group of researchers in Germany have published the results of a study designed to evaluate whether treating dogs presenting with HGE with amoxicillin/clavulanic acid affects the clinical course or outcome.

Study design
This prospective, placebo-controlled, blinded study involved 60 dogs with HGE at the University of Munich that had an acute onset of bloody diarrhea (> 3 days). There was a balanced number of males and females, with a median age of 5.4 years and body weights ranging from 1.6 to 41.6 kg. Those that had been pretreated with antibiotics or any drug that may cause mucosal irritation, that had any signs of sepsis, or that had hemorrhagic diarrhea because of an underlying disease condition were excluded. Fecal cultures were performed on all dogs, and those that had positive results for enteropathogenic bacteria were also excluded from the study.

Diagnostic tests included an abdominal ultrasonographic examination, serum chemistry profile, clotting profile, bile acid concentration measurement, fecal examination for parvovirus and parasites including Giardia species, and culture for enteropathogenic bacteria. Additionally, blood cultures were performed.

The dogs were randomly divided into either a placebo or treatment group. Dogs in the treatment group received amoxicillin/clavulanic acid for seven days. All other supportive therapies (fluids, antiemetics, gastric antacids, and disseminated intravascular coagulation prophylaxis) did not differ significantly between the two groups. Dogs were hospitalized for at least three days, and the antibiotic was administered by subcutaneous injection once daily (7 mg/kg) while the dogs were in the hospital and orally twice daily (12.5 mg/kg) after discharge. Dogs in the placebo group were given a placebo tablet at home.

The severity of clinical signs was evaluated based on a modified version of the canine inflammatory bowel disease index, ranking parameters such as attitude, appetite, vomiting, stool consistency and frequency, and dehydration. Scores ranged from 0 to 3, with 0 representing normal and 3 indicating severe clinical signs. The length of hospitalization and mortality rates was also compared between the two groups.

Study results and implications
No complications were attributed to antibiotic therapy, and both groups saw rapid improvement in clinical signs during the first 48 hours. The duration of hospitalization was also similar. In fact, no significant laboratory variations between the two groups occurred, and, over the course of the disease, there were no differences in stool consistency or stool frequency. Even when concentrating on patients with positive blood culture results (5%), there was no statistical difference between outcome and assigned treatment group. None of the dogs with a positive culture result had clinical signs of sepsis nor had to be unblended and removed from the study. Moreover, no benefit was seen from antibiotic therapy in these dogs.

Based on the results of this study, it would appear that HGE is not the result of a primary bacterial infection, the involved bacteria are not vulnerable to amoxicillin/clavulanic acid, or the bacterial infection or enterotoxin involved is self-limiting. Since the cause of HGE is unknown and it is often a diagnosis of exclusion, these findings suggest that further research is necessary to identify which patients may benefit from antimicrobial therapy and in which cases it is inappropriate.

Unterer S, Strohmeyer K, Kruse BD, et al. Treatment of aseptic dogs with hemorrhagic gastroenteritis with amoxicillin/clavulanic acid: a prospective blinded study. J Vet Intern Med 2011;25(5):973-979.

Link to abstract: http://onlinelibrary.wiley.com/doi/10.1111/j.1939-1676.2011.00765.x/abstract