The CABI Trial: an Unblinded Parallel Group Randomised Controlled Feasibility Trial of Long-Course Antibiotic Therapy (28 Days) Compared with Short Course (≤ 10 Days) in the Prevention of Relapse in Adults Treated for Complicated Intra-Abdominal Infection

Relapse after complicated intra-abdominal infection (cIAI) remains common after treatment. The optimal antibiotic treatment duration for cIAIs is uncertain, especially in cases where source control is not achieved. We hypothesised that in patients with cIAIs, regardless of source control intervention, there would be a lower relapse rate with long-course antibiotics (28 days) compared with short course (≤ 10 days). We piloted a trial comparing ≤ 10-day with 28-day antibiotic treatment for cIAI. A randomised controlled unblinded feasibility trial was conducted. Eligible participants were adult patients with a cIAI that were diagnosed ≤ 6 days prior to screening. Randomisation was to long-course (28 days) or short-course (≤10 days) antibiotic therapy. Choice of antibiotics was determined by the clinical team. Participants were followed up for 90 days. Primary outcomes were willingness of participants to be randomised and feasibility of trial procedures. In total, 172 patients were screened, 84/172 (48.8%) were eligible, and 31/84 (36.9%) were randomised. Patients were assigned to either the short-course arm (18/31, 58.0%) or the long-course arm (13/31, 41.9%). One patient in the short-course arm withdrew after randomisation. In the short-course arm, 4/17 (23.5%) were treated for a cIAI relapse vs 0/13 (0.0%) relapses in the long-course arm. Protocol violations included deviations from protocol-assigned antibiotic duration and interruptions to antibiotic therapy. This feasibility study identified opportunities to increase recruitment in a full trial. This study demonstrates completion of a randomised controlled trial to further evaluate if the optimum antibiotic duration for cIAIs is feasible. ClinicalTrials.gov Identifier: NCT03265834