The first line therapy for an initial episode of CDI (Clostridium difficile infection) is 10-14 days of oral vancomycin which is now recommended over metronidazole in the 2018 guidelines from the Association of Medical Microbiologists and Infectious Diseases of Canada (AMMI). Although response rates for the treatment of a first episode of CDI now approach 90%, approximately 25% of patients who have a complete response will develop recurrence (rCDI) within 8 weeks. Doctors' ability to predict recurrence is evolving, but remains very limited.

The investigators hypothesize that by extending initial vancomycin therapy with a 2-week tapering regimen this will reduce the risk of rCDI. Starting at the end of the initial 14 days of therapy, participants will be randomized to receive an additional 14-days of placebo or vancomycin taper (125 mg orally twice daily x 7 days followed by 125 mg orally once daily x 7 days). This taper was chosen as it represents two steps of a commonly used 4-week vancomycin taper.

The investigators' proposal to evaluate the extension of initial treatment from 14 to 28 days with a tapering dose of vancomycin represents a practical clinical trial that capitalizes on oral vancomycin's safety profile, worldwide availability, and relatively low cost.

STUDY POPULATION

This is a multi-centre study involving institutions in British Columbia, Ontario, Quebec and Newfoundland. The study population will be drawn from patients cared for as inpatients or outpatients at the participating hospitals. Such patients will have a test positive for C. difficile and will be receiving treatment. The trial will involve only adult patients 18 years of age and older.

Criteria for Recruitment

The microbiology laboratory will notify the study team about a positive CDI test via telephone, email, or fax. The nature of recruitment will then depend on the inpatient status of the patient at the time of the test.

Inpatients:

Pre-existing approval for approaching patients for this study will be obtained from the relevant department heads. The study team will speak with a member of the inpatient treating team (resident physician or faculty physician as appropriate) to determine if the patient is appropriate for recruitment. If this seems to be the case, the patient's file will be rapidly screened to determine eligibility and if the patient is eligible they will be approached for consent.

Outpatients:

The physician who ordered the C. difficile test will be contracted to determine if the patient is appropriate for recruitment. At the invitation of this physician, the investigators will then contact the patient via telephone to evaluate suitability for inclusion and arrange an intake visit.

RANDOMIZATION

For patients who have enrolled in the study, randomization will occur centrally at McGill via an existing internet application and will be performed by permuted block with randomized block sizes. This randomization will be stratified for first episode or first recurrence at study entry to ensure these factors are properly balanced.

TRIAL SCHEDULE

• Day 1: Patient diagnosed with C. difficile and started on standard of care oral vancomycin treatment -> Determine eligibility and obtain permission for approach
• Day 7-10 (Patient's C. difficile has improved and meets eligibility): Consent obtained; randomization; distribution of study drug for day 15 start -> Collection of demographics
• Day 15-28 -> Receipt of study therapy
• Day 28: In person or remote visit
• Day 56: In person or remote visit -> Primary outcome determined, quality of life questionnaire
• Day 90: Study ends for the patient -> Secondary outcomes can be determined
• weekly until Day 56: Brief questionnaire -> By email/text/phone
• biweekly after Day 56: Brief questionnaire -> By email/text/phone
• Ad hoc: If patient has symptoms of recurrence of C. difficile -> Review by ID physician in clinic if possible, otherwise usual doctors or emergency room

Patients will be able to come be assessed for potential relapse by infectious diseases physicians at each site (who may or may not be a part of the study) or could see their usual doctors.

SAMPLE SIZE AND STATISTICAL METHODS

The initial estimates were a risk of recurrence in the control group of 25% and in the intervention group of 15%. With 80% power and an overall alpha of 0.05, it would require 496 patients (rounded to 500) to demonstrate superiority.

After the recruitment of 50 patients, the analytic plan was modified to use a Bayesian framework on April 3rd, 2023, prior to completion of study enrolment and before data were locked and blinded for analysis. This was done to allow for earlier stopping while preserving the overall type 1 error rate and maximal sample size in response to an update to the Infectious Diseases Society of America guidelines for the treatment of C. difficile, which were changed to recommend fidaxomicin as first line therapy in place of vancomycin.

We used adaptR to simulate 50,000 2-armed trials under both the null and alternative hypotheses using the funded 500 patient sample size and interim analyses at 125, 250 and 500 patients. The thresholds for superiority (relative risk <1) were 99% at the first analysis and 97.5% at subsequent analyses. A futility analysis was included whereby the trial would be stopped if there was less than a 15% probability of at least a 4% absolute risk reduction (number needed to treat, NNT ≤ 25). These simulations estimated an overall type 1 error rate of 5.1% with 72.6% power and a median expected sample size of 250 patients.

All binary outcomes were analysed using a Bayesian Generalised Linear Model (binomial family, log link) which yields log relative risk (RR) with 95% Bayesian credible intervals (CrI). These were exponentiated to give risk ratios. Priors were minimally-informative [N~ (0,100)]. Stratification was included in the model and we ran 4 chains of 50,000 Markov Chain Monte Carlo simulations.

Inclusion Criteria:

• All consecutive adult patients (inpatients and outpatients) who have a treated first episode or first recurrence of CDI.
• CDI will be defined by a positive PCR for toxin gene and/or detection of toxin by EIA or CCA along with three or more episodes of diarrhea within 24 hours
• Patients with a positive test with less than three bowel movements may be included if they initially presented with ileus or if they had pseudomembranous colitis visualized on colonoscopy

Exclusion Criteria:

• Clinical:

  1. Toxic megacolon at presentation not resolved by day 10

  2. For the current episode of CDI: use of metronidazole monotherapy*, fidaxomicin, fecal microbiota transplant or intravenous immunoglobulins

     *Participants may be eligible if they are initially treated with metronidazole but switch to oral vancomycin within 3 days (i.e. maximum 3 days of metronidazole monotherapy).

  3. Previous or current colectomy

  4. Severe allergy/intolerance to oral vancomycin

  5. Patient is expected to die within 3 months from another disease or is expected to be admitted to a palliative care unit

  6. Failure to achieve clinical cure (as above) by day 10

  7. More than 2 episodes of C. difficile in the last 5 years.

  8. Documented history of sensorineural hearing loss (other than presbycusis and noise induced hearing loss). The following patients with documented previous subtypes of sensorineural hearing loss will be excluded from the trial: Menière's disease, multiple sclerosis affecting auditory nerves, otic syphilis, viral cochleitis, autoimmune disorders, previous drug induced hearing loss, and otherwise unexplained sudden sensorineural hearing loss (SSNHL)

  9. Known pregnancy or planning to become pregnant during the study period

  10. Women who are breast feeding

• Administrative:

  1. Expected transfer to a palliative care unit or non-study hospital;
  2. No provincial health insurance
  3. Previously enrolled
  4. No reliable means of outpatient contact
  5. Incompetent without healthcare proxy
  6. Patient stated inability to come to follow up appointments.

We will conform to our institutional policies and the policy of the accepting journal.

Double-blinded placebo-controlled randomized controlled trial:

A double blind and placebo will be used because the knowledge of being on active drug might influence patient reporting on gastrointestinal symptoms or physician interpretation of such symptoms leading to asymmetrical workup of CDI recurrence and hence bias in the results.

To avoid other sources of bias post-randomization, patients, research personnel, investigators, endpoint adjudicators, and study analysis will all remain blinded to the intervention status until completion of the analysis and reporting of results. Analysis will be performed by intention to treat.