The use of metronidazole in adult dogs with acute onset, uncomplicated, diarrhoea

PICO question 
In adult, non-geriatric, dogs with acute onset (<7 days duration) uncomplicated diarrhoea does the addition of metronidazole to a supportive care protocol such as dietary modification or probiotics (excluding other antimicrobials) reduce the time to resolution of diarrhoea compared to supportive care protocols alone? 
  
Clinical bottom line 
Category of research question 
Treatment 
The number and type of study designs reviewed 
Four studies were included in this appraisal. Two prospective, double blinded, placebo controlled clinical trials, one prospective treatment trial and one retrospective longitudinal observational study 
Strength of evidence 
Weak 
Outcomes reported 
One study found a shortened duration of clinical signs (by 1.5 days; p = 0.04) in the metronidazole treated group compared to control. However, a separate study found no significant difference between control and metronidazole groups in the regards to resolution of clinical signs. 
One study demonstrated a long standing (>28 day) negative impact of metronidazole treatment on gut microbiome with no difference in time to resolution of clinical signs when compared with faecal matter transplant 
Conclusion 
The current evidence for the superiority of metronidazole compared to supportive treatment alone is weak and at this time there is no evidence-based rationale for its use in cases of uncomplicated, acute, canine diarrhoea. Furthermore, the negative implications of metronidazole on the intestinal microbiome have been found to be long standing (>28 days as a minimum) and should not be discounted by the prescribing clinician 
  
How to apply this evidence in practice 
The application of evidence into practice should take into account multiple factors, not limited to: individual clinical expertise, patient’s circumstances and owners’ values, country, location or clinic where you work, the individual case in front of you, the availability of therapies and resources. 
Knowledge Summaries are a resource to help reinforce or inform decision making. They do not override the responsibility or judgement of the practitioner to do what is best for the animal in their care. 
  



The evidence
Until as recently as 2019 the evidence basis for the use of metronidazole in the face of uncomplicated acute canine diarrhoea (UACD) and its superiority to supportive treatment alone (dietary modification, probiotics and more recently faecal matter transplant) has been anecdotal. Four papers were found to be fully or partially relevant to the PICO question; two randomised, double blinded placebo-controlled trials (Shmalberg et al., 2019;and Langlois et al., 2020), one prospective controlled treatment trial (Chaitman et al., 2020) and one retrospective observational study (Singleton et al., 2019). All four studies measured time to resolution of diarrhoea. Other factors considered included faecal microbiome and metabolome diversity (Chaitman et al, 2020). The evidence for the PICO question was found to be weak and at this time there is insufficient evidence to suggest metronidazole is superior in reducing the duration of clinical signs of UACD when compared to supportive measures alone. Sample size: 63 dogs enrolled, 60 completed the study. Three dogs were withdrawn and not included in the final analysis due to either a significant parasite burden (n = 1, metronidazole group) or failure of owners to give the assigned study treatment (n = 2, one each in probiotic and placebo group). Patients were enrolled until there were 20 cases present in each group based on prestudy power calculations. Clients were requested to fast the patient for 24 hours before a gradual reintroduction of food over next 24 hours. Patients were randomised to a treatment group via pre-study randomisation schedule. Both the owner and clinician were blinded to treatment administered.
The study was unblinded after enrolment of the 60 dogs to perform statistical analysis.
Outcome studied: Time to normal faeces with assessment of faecal consistency, faecal score (based on the WALTHAM™ Faeces Scoring System), defaecation frequency, straining.

Main findings: (relevant to PICO question):
Dogs were withdrawn from the study due to owner non-compliance, abnormalities noted on post-enrollment laboratory or PCR testing or high faecal worm egg count (total withdrawn = 3) Patient age: • Probiotic group: 5.3 ± 3.2 years; • Metronidazole group: 5.7 ± 3.7 years; • Placebo group: 5.7 ± 3.9 years. There was no statistically significant improvement in time to clinical resolution of the clinical signs in any treatment group (p = 0.17). Time to normal faecal consistency: • Probiotic group: 3.5 ± 2.2 days; • Metronidazole group: 4.6 ± 2 days; • Placebo group: 4.8 ± 2.9 days. No adverse effects were observed in any treatment group. No dog required rescue treatment.

Limitations:
• No standardised treatment protocol so likely multiple confounding effects between cases, although study design and statistical analysis has been structured to minimise this effect. • Clients were provided a financial incentive which may influence their interpretation. • Low case numbers in each treatment group, although the treatment group sizes were based on pre-study power calculations. • No control of diet. • No microbiome or metabolome testing.

Singleton et al. (2019)
Population: Analysis of electronic health records from 179 volunteer veterinary practices in the UK that participate in the Small Animal Veterinary Surveillance Network. Cases booked in from 1 April 2014 to 31 January 2017, included all canine consultations that had been classified as 'gastroenteritis' as the main presenting complaint that also had a completed questionnaire pertaining to clinical signs, diagnostics and advice to the client. Inclusion criteria: acute, first presentation diarrhoea of <2 days duration. Exclusion criteria: euthanasia on presentation (n = 6) and lost to follow-up (n = 754).
Sample size: Initial review of medical records found a total of 12,455 cases of 'gastroenteritis' that also included the augmented questionnaire. Of those 3,192 were found to fit the above inclusion criteria. A further three cases were excluded due to inaccurate date of birth entry. Of those 3,189 a further 760 were excluded for aforementioned reasons leaving a total of 2,429 cases used within the modelling dataset.

Study design:
Retrospective longitudinal observational study.
Outcome studied: Cases considered as resolved if they did not return to the practice for a 'gastrointestinal' reason between 11-30 days of initial presentation. Any case re-presenting within 10 days of initial presentation was manually checked to ensure no mention of diarrhoea in case notes.

Main findings: (relevant to PICO question):
Total of 763 excluded from the analysis. Reasons for this include euthanasia on presentation (n = 6), lost to follow-up (n = 754) and inaccurate birth date (n = 3). Large variation in severity of clinical presentation: mild cases (n = 2665) moderate cases (n = 507) and severe cases (n = 17). Prescribing of antibiotics: • Dogs with blood in diarrhoea were more frequently prescribed systemic antibiotics as were those that were pyrexic (haemorrhagic diarrhoea odds ratio ) and was not significant when considering day 10 resolution (p = 0.95). Resolution of clinical signs within 30 days of initial presentation: • Dietary modification advice and gastrointestinal nutraceuticals were positively associated with resolution of signs (OR 2.8, 95% CI 1.3-6.1) • No such association was found for pharmaceutical agents including antibiotics.

Limitations:
• Retrospective study -limitations of retrospective studies are extensive but include lack of control for confounding variables, ability to only infer association not causation, misclassification bias, convenience recruitment which can lead to population not being representative of general population amongst others. • Calculation of percentage antibiotic prescribing events not expressly documented within the paper. • Lack of complete clinical records (for example inconsistent body temperature recording) for all cases. • Large loss to follow-up although this may be associated with a positive outcome (i.e. case does not return to the practice as clinical signs have resolved) this represents an assumption and as such definitive positive or negative associations may be over or under represented. • Assumption of resolution of clinical signs based on lack of follow-up appointment. • Lack of standardisation: wide variety of treatments administered leading to potential for significant confounding effects. Outcome studied: Evaluation of clinical signs: by assessment of faecal consistency by a board certified clinician using Purina® Faecal Scoring Chart on days 0, 7 and 28 (lower score represents a normal stool consistency). Analysis of faecal microbiota: assess by use of quantitative PCR, (qPCR) dysbiosis index and 16s ribosomal RNA (rRNA) Gene sequencing. Analysis of faecal metabolome: measurement of unconjugated bile acids and untargeted metabolomics approach.

Main findings: (relevant to PICO question):
Faecal scores: • Faecal scores decreased significantly from day 0 to day 7 and day 28 in both treatment groups (p <0.01 in both cases). • Faecal scores significantly lower in FMT group when compared to MET group on day 28 (p = 0.04). Faecal dysbiosis index (DI): • No significant difference between treatment groups on day 0. Significant difference between acute diarrhoea dogs compared to healthy controls (higher DI in acute diarrhoea group; p <0.001). • Dogs after FMT showed significant decrease in DI (p <0.05).
• Dogs in MET group showed significant increase in DI (p <0.05). • Abundance of Faecalibacteria (associated with health) increased in FMT and significantly higher compared to MET at days 7 and 28 (p <0.05). However significantly lower in both acute diarrhoea treatment groups compared to controls (p <0.05). • hiranois (a bacterial species important for conversion of primary to secondary bile acids): no significant difference was found between control and FMT group at day 28. MET group showed significant decrease in C. hiranois when compared to control dogs at both day 7 and day 28 (p<0.05). 16s rRNA gene sequencing: • Significant decrease in alpha diversity in MET group compared to controls (p <0.05). • Day 28 FMT group and control no significant difference in microbial communities (p = 0.06). • Day 28 MET group still had significantly different microbial communities (based on weighted distances) compared to controls (p = 0.001). Faecal bile acid concentrations: • FMT led to significant decrease in primary bile acids at day 28 compared to day 0 (p <0.05). These were also lower, but not significantly, at day 7 in this group. • MET led to significant increase in primary bile acids at day 7 (p <0.05). Untargeted faecal metabolomics: • FMT dogs clustered closer to controls when compared to MET dogs at day 28.

Limitations:
• Not randomised. • Not blinded -or at least not reported to be allowing for interpretation bias by the assessor. • Small treatment groups. • Lack of placebo. Whilst a healthy control population was included a negative control population was not. • FMT protocol not standardised for all patients.
• No faecal scores provided for healthy control population.

Langlois et al. (2020)
Population: Client owned dogs presenting to a University Veterinary Centre (Michigan, USA) for acute diarrhoea with or without vomiting. Intervention details: Dogs randomly allocated to either placebo n = 17 (capsule containing only microcrystalline cellulose) or metronidazole group n = 14 (10-15 mg/kg PO). Either intervention given q12 hour for 7days. Owners also requested to withhold food for initial 12 hours after enrolment and gradually resume feeding of normal diet over subsequent 12-24 hours. Dogs that had vomiting also received a single dose of maropitant (Cerenia®, Zoetis) 1 mg/kg SQ. Administration of crystalloid fluids was also permitted. The use of antacids, antidiarrhoeals or any newly prescribed medications was not permitted for the duration of the study unless

Limitations:
• Unvalidated method of stool consistency monitoring as a human based chart rather than a veterinary one. • Referral filter bias.

Appraisal, application and reflection
The available evidence is split between two randomised prospective double blinded clinical trials (Shmalberg et  clinical signs if the patient does not represent to the clinic for GI signs within 30 days. However, there is no standardisation in the assessment of this outcome which, given its subjective nature, does lend towards observer and assessment bias. Especially given that in the three studies that utilised a faecal consistency chart  2019) study assessed the prescribing habits of UK first opinion practitioners when faced with a case of UACD in general practice and of the 2,429 cases that were including in the analysis 52.5% of those were prescribed antibiotics within 10 days of initial presentation. Of those cases metronidazole was the most commonly prescribed (47% of antibiotic prescribing cases). Furthermore, the study identified 1,050 cases (35.7%) where a patient was normothermic, with mild non-haemorrhagic diarrhoea and still prescribed antibiotics. However, the multivariable analysis of the records in this paper found no positive correlation between the prescribing of pharmaceutical agents (including antibiotics) and resolution of clinical signs. Whilst the limitations of this paper, given its retrospective nature, large loss to follow-up and inconsistency in record keeping, are significant, the large population size adds strength to the clinical utility of this information. This lack of positive correlation between antibiotic use and resolution of clinical signs was mirrored in both the  the conversion of primary bile acids to secondary bile acids) when compared to healthy controls suggestive of ongoing alteration of intestinal function, despite normalisation of faecal consistency.
Standardisation of treatment protocols was lacking across the three prospective treatment trial papers as well as the retrospective longitudinal study. When considering the Shmalberg et al. (2019) paper there was no standardisation in regards to the administration of crystalloid fluids, fenbendazole or maropitant and no standardisation of diet -owners do not appear to have been requested to continue to feed a normal diet and so there is potential for variation from normal diet which may have a confounding effect on duration of clinical signs. The Langlois et al. (2020) paper has similar potential for confounding effects with the administration of crystalloid fluids and maropitant although additional oral medications were not prescribed to these patients. There was a lack of standardisation of treatment in the Chaitman et al. (2020) paper in regards to both maropitant use and dietary advice. Maropitant, a NK1 antagonist is a generally very well tolerated medication but diarrhoea has been described as a rare side effect in dogs (Zoetis, 2019). However, a study assessing the use of maropitant in the face of doxorubicin associated delayed vomiting found a reduction in frequency of patients developing diarrhoea, hypothesising that there may be a role of substance P in the development of diarrhoea -or at least diarrhoea associated with chemotherapy (Rau et al., 2010) although no further studies have evaluated this link. So, whilst it is unlikely to have a significant impact on the outcome of these studies, its potential as a confounding variable cannot be discounted. However, clinically the use of maropitant is unlikely to be detrimental in a case of acute diarrhoea and given its potent anti-emetic effects its use should not be discounted when faced of a concurrently nauseous patient. There is also considerable variation in the Finally, although out of the scope of this Knowledge Summary, it feels prudent to touch upon the results pertaining to probiotics in these studies. The utility of probiotics was not found to be superior when compared to either placebo or metronidazole treatment in the Shmalberg et al. Whilst the available literature is limited, at this time there is insufficient evidence to conclude a benefit to the prescribing of metronidazole in UACD in favour of supportive measures alone. There is also evidence to suggest that the use of metronidazole can have long-term detrimental implications for the gut microbiome and metabolome. Therefore, based on this current review of the available evidence, metronidazole would not be recommended as a first-line treatment in a case of UACD. There would be benefit for further studies of a higher power (prospective, randomised, blinded placebo-controlled treatment trial) with closer standardisation of protocol and larger treatment groups. Furthermore, the utility of both subjective, but validated, faecal consistency scoring and quantitative microbiome/metabolome analysis should be considered as well as multivariant analysis in an attempt to control for confounding variables to better ascertain appropriate, evidence-based treatment protocols for the management of UACD.