Antimicrobial Stewardship (AMS)

Resources to help you ensure the safe and effective use of antimicrobials in NSHA patients.

Clostridioides (Clostridium) difficile Infection in Adults

Clostridioides difficile infection (CDI) is defined by the presence of:

  • Unexplained and new-onset 3 or more unformed stools in 24 hours* AND
    • Stool test positive for C. difficile toxins OR
    • Colonoscopic or histopathologic findings revealing pseudomembranous colitis

* Patients with severe disease may not have loose stools if they have toxic megacolon or ileus.

Last reviewed December 2023

  • If CDI is suspected, send a stool sample for testing and initiate contact precautions plus (+): Contact Precautions with the addition of an Enteric Clean.
  • Empiric therapy for CDI should be started while awaiting diagnosis if:
    • Substantial delay in laboratory confirmation is expected
    • Patient symptoms are consistent with severe CDI
  • Assess medications or interventions that are known to cause diarrhea, such as laxatives and enteral feeds, etc.
  • Do not test stool of asymptomatic patients (3%-14% carriage in adults admitted to hospital).
  • Test of cure is not recommended since testing can remain positive even after successful treatment.

Last reviewed December 2023

  • Discontinue antimicrobials if possible. Consider switching to an antimicrobial associated with a lower risk for CDI if antimicrobials are required.
  • Consider discontinuing proton pump inhibitor therapy if appropriate.
  • Avoid opioids and antimotility agents (e.g., loperamide).
  • No antimicrobial treatment for CDI is required if diarrhea has resolved.*

*Exception - cases where ileus may be possible (e.g., severe and complicated disease)

  • Infectious Diseases & Surgery consultation is recommended for severe and complicated CDI.
  • Probiotics are not currently recommended for the treatment or prevention of CDI.

Last reviewed December 2023

  • Consider consultation with Infectious Diseases if severe allergy to vancomycin
  • Fidaxomicin may be used in the setting of vancomycin allergy. There is increased risk of fidaxomicin hypersensitivity with macrolide allergy history.



Category Severity criteria Treatment recommendation

Mild to moderate

  • WBC less than or equal to 15 x 109/L, and
  • Creatinine less than or equal to 1.5 x baseline, and
  • Age less than or equal to 60 years
  • Vancomycin 125 mg PO QID for 10 days


  • Metronidazole 500 mg PO TID for 10 days 
    • Should be reserved for patients with mild diarrhea if the cost of vancomycin is prohibitive. 

Severe, uncomplicated

  • WBC greater than 15 x 109/L or
  • Creatinine greater than 1.5 x baseline or
  • Age greater than 60 years or
  • Hypoalbuminemia


  • Vancomycin 125 mg PO QID for 10 days 
Severe, complicated
  • Hypotension 
  • Shock
  • Ileus 
  • Megacolon
  • Vancomycin 500 mg PO/NG QID, may reduce dose to 125 mg PO/NG when no longer critically ill to complete a total course of 14 days AND 
  • Metronidazole 500 mg IV Q8h until no longer critically ill AND
  • If paralytic ileus, consider adding vancomycin rectally: 500 mg in 100 mL normal saline per rectum Q6h as a retention enema
  • Consider surgical consultation


Category Severity criteria Treatment recommendation

First recurrence (2nd episode),
mild to moderate

  • WBC less than or equal to 15 x 109 / L, and 
  • Creatinine less than or equal to 1.5 baseline, and
  • Age less than or equal to 60 years 
  • Preferred: Vancomycin 125 mg PO QID for 14 days OR 
    • Consider fidaxomicin 200 mg PO BID for 10 days in patients at high risk of recurrence* and cost is not prohibitive OR
    • Alternative: Metronidazole 500 mg PO TID for 14 days
      • Should only be considered if metronidazole not used for initial episode and if the cost of vancomycin or fidaxomicin is prohibitive.

First recurrence (2nd episode),
severe, uncomplicated

  • WBC greater than 15 x 109/L or
  • Creatinine greater than 1.5 x baseline or
  • Age greater than 60 years or
  • Hypoalbuminemia


  • Vancomycin 125 mg PO QID for 14 days OR
  • Consider fidaxomicin 200 mg PO BID for 10 days in patients at high risk of recurrence* and cost is not prohibitive.

*Risk factors for recurrent CDI include:

  • Greater than 60 years of age
  • Significant immunocompromise
  • Hospitalized for severe C. difficile infection within the previous 3 months
  • Current use of:
    • Antibiotics, proton pump inhibitors, antimotility agents and opioids

Second (3rd episode) or subsequent recurrence

Vancomycin Taper
  • 125mg PO QID x 14 days then
  • 125mg PO TID x 7 days then
  • 125mg PO BID x 7 days then
  • 125 mg PO daily x 7 days then
  • 125mg PO every 2 or 3 days for 2-8 weeks


Fidaxomicin 200mg PO BID for 10 days

  • Consider consulting Infectious Diseases following one failed vancomycin taper

Last reviewed December 2023

1. Loo VG, Davis I, Embil J, Evans GA, et al. Association of Medical Microbiology and Infectious Disease Canada treatment practice guidelines for Clostridium difficile infection. Journal of the Association of Medical Microbiology and Infectious Disease Canada. 2018; 3(2): 71-92.

2. McDonald LC, Gerding DN, Johnson S, Bakken JS, et al. Clinical Practice Guidelines for Clostridium difficile Infection in Adults and Children: 2017 Update by the Infectious Diseases Society of America (IDSA) and Society for Healthcare Epidemiology of America (SHEA). Clin Infect Dis. 2018; 66(7):e1-e48.

3. Van Hise NW, Bryant AM, Hennessey EK, Crannage AJ, et al. Efficacy of Oral Vancomycin in Preventing Recurrent Clostridium difficile Infection in Patients Treated With Systemic Antimicrobial Agents. Clin Infect Dis. 2016 Sep 1;63(5):651-3.

4. Appaneal HJ, Caffrey AR, LaPlante KL. What is the role for metronidazole in the treatment of Clostridium difficile infection? Results from a national cohort study of Veterans with initial mild disease. Clin Infect Dis. 2018; Dec 18 [Epub ahead of print].

5. Fabre V, Dzintars K, Avdic E, Cosgrove SE. Role of Metronidazole in Mild Clostridium difficile Infections. Clin Infect Dis. 2018;67(12):1956-1958.

Last reviewed December 2023

Intra-abdominal Infections (IAIs) in Adults

  • IAI: infection involving any of the organs or organ spaces in the abdominal cavity
  • Community-acquired: acquired outside the healthcare setting 
  • Healthcare-associated: more than 48 hours after admission, recent hospitalization, dialysis, or resident of long term care facility. Late onset (more than 5 days after admission) is associated with more resistant microorganisms.

Last reviewed July 2020

  • Streptococcus  spp., Enterobacterales (e.g., E. coli, Klebsiella spp., Proteus spp.), anaerobes 
  • Health-care associated: 
  • Pseudomonas aeruginosa, Citrobacter spp., Enterobacter spp., ESBL-producing Enterobacteriaceae , Enterococcus spp., Candida spp.

Last reviewed July 2020

  • Imaging: modality depends on the clinical diagnosis. 
    • If a perforated viscus is suspected, plain X-ray (supine, upright, and lateral decubitus) should be done to look for free air
    • Ultrasound or CT is usually required to diagnose or characterize organ infections (e.g. cholecystitis, cholangitis, liver abscess) and abscesses
  • Cultures:
    • Blood cultures (2 aerobic & anaerobic sets): if patient is septic or immune-compromised
    • Intra-operative abscess/tissue samples or percutaneous aspirates for culture, even if the patient has been on antimicrobials. For increased  yield, purulent fluid and/or tissue in a sterile container are preferred over swabs of fluid and tissue.
    • Avoid taking cultures from drains/fistulae: the microbes isolated are likely to represent colonization and not clinical infection.

Last reviewed July 2020

  • Source control is necessary; if symptoms present for a few days, can delay antibiotics if stable and pending source control procedure/ specimen collection
  • Lack of clinical improvement should prompt further source control, rather than prolonging or changing antimicrobial therapy in the absence of culture results  to support a change in antimicrobial management
  • Consider Candida coverage: 
    • Yeast are the only microorganism identified on Gram stain/culture from infected peritoneal fluid or tissue
    • Persistent intra-abdominal collections/infection and has had a prolonged course of antibiotics (tertiary peritonitis)
      • Fluconazole preferred in most cases
      • Echinocandin if non-albicans yeast or fluconazole exposure within past 30 days


Last reviewed July 2020

  • Cefazolin or ceftriaxone are usually safe in those with a penicillin allergy unless severe delayed skin reaction/organ dysfunction (e.g. Stevens-Johnson syndrome, toxic epidermal necrolysis, drug reaction with eosinophilia and systemic symptoms) See Beta-lactam allergy section of the handbook.    
  • Carbapenem
    • Use imipenem rather than meropenem if covering Enterococcus faecalis in setting of polymicrobial infection
    • If all beta-lactams contraindicated: consider ID consult
      • Ciprofloxacin or aminoglycoside (not for abscess) + metronidazole
      • Vancomycin if Enterococcus coverage required

Last reviewed July 2020

Last reviewed July 2020

1. Mazuski JE, Tessier JM, May AK, et al. The Surgical Infection Society Revised Guidelines on the Management of Intra-Abdominal Infection. Surg Infect (Larchmt). 2017 Jan;18(1):1-76.

2. Sawyer RG, Claridge JA, Nathens AB, et al. Trial of short-course antimicrobial therapy for intraabdominal infection. N Engl J Med. 2015 May 21;372(21):1996-2005.

3. Solomkin JS, Mazuski JE, Bradley JS, et al. Diagnosis and Management of Complicated Intra-abdominal Infection in Adults and Children: Guidelines by the Surgical Infection Society and the Infectious Diseases Society of America. Clin Infect Dis 2010; 50: 133-64.

Last reviewed July 2020