Assessing the feasibility of a platform trial for Gram negative bloodstream infections: results from the vanguard phase of BALANCE+

OBJECTIVES: Gram negative bloodstream infections (GN BSI) are a leading cause of mortality worldwide, and antibiotic treatment approaches remain understudied. BALANCE+ is a perpetual Bayesian adaptive platform trial to test multiple treatment questions for hospitalised patients with GN BSI. The vanguard phase objective was to test the feasibility of the main trial. DESIGN: Adaptive platform trial with five initial domains of investigation, each with open label 1:1 randomisation. SETTING: Ten hospitals across four Canadian provinces. PARTICIPANTS: Individuals admitted to hospital with blood cultures yielding Gram negative bacteria. INTERVENTIONS: The five initial domains of investigation included: antibiotic de-escalation versus no de-escalation; oral transition to beta-lactam versus non-beta-lactam treatment; routine versus no routine follow-up blood cultures (FUBCs); central vascular catheter replacement versus retention; and, ceftriaxone versus carbapenem treatment for low risk AmpC organisms. PRIMARY OUTCOME MEASURES: Domain-specific recruitment rates and protocol adherence. RESULTS: During the vanguard phase, 719 patients were screened, of whom 563 (78.3%) were eligible, with 179 (31.8%) enrolled into the platform. The platform recruitment rate was 1.37 patients/site-week. Recruitment varied by domain: routine versus no FUBC domain 1.23 patients/site-week; oral beta-lactam versus non-beta-lactam domain 0.48; de-escalation versus no de-escalation domain 0.28; low risk AmpC domain 0.02; catheter replacement versus retention domain 0.01. Domain specific protocol adherence rates were 145/158 (91.8%) for routine versus no routine FUBC, 53/60 (88.3%) for oral beta-lactam versus non-beta-lactam, 26/33 (78.8%) for de-escalation versus no de-escalation, 3/3 (100%) for low risk AmpC, and 0/1 (0%) for line replacement versus retention. There was complete ascertainment of all study outcomes in hospital 170/170 (100%) and near complete ascertainment at 90 days 162/170 (95.3%). CONCLUSIONS: The vanguard phase demonstrated overall trial feasibility by recruitment rate and protocol adherence, with differences across interventions, leading to a transition to the main BALANCE+ platform trial with minimal protocol modifications. TRIAL REGISTRATION NUMBER: NCT05893147.