Win ratio analyses of piperacillin-tazobactam versus meropenem for ceftriaxone non-susceptible Escherichia coli or Klebsiella pneumoniae bloodstream infections: Post-hoc insights from the MERINO trial.

BACKGROUND: Clinical trials of treatments for serious infections commonly use the primary endpoint of all-cause mortality. However, many trial participants survive their infection and this endpoint may not truly reflect important benefits and risks of therapy. The win ratio uses a hierarchical composite endpoint that can incorporate and prioritise outcome measures by relative clinical importance. METHODS: The win ratio methodology was applied post-hoc to outcomes observed in the MERINO trial, which compared piperacillin-tazobactam with meropenem. We quantified the win ratio with a primary hierarchical composite endpoint, including all-cause mortality, microbiological relapse and secondary infection. A win ratio of one would correspond to no difference between the two antibiotics, while a ratio less than one favors meropenem. Further analyses were performed to calculate the win odds and to introduce a continuous outcome variable in order to reduce ties. RESULTS: With the hierarchy of all-cause mortality, microbiological relapse and secondary infection, the win ratio estimate was 0.40 (95% CI: 0.22, 0.71; p=0.002), favoring meropenem over piperacillin-tazobactam. However, 73.4% of the pairs were tied due to the small proportion of events. The win odds, a modification of the win ratio accounting for ties, was 0.79 (95% CI: 0.68, 0.92). The addition of length of stay to the primary composite, greatly minimised the number of ties (4.6%) with a win ratio estimate of 0.77 (95% CI: 0.60-0.99; p=0.04). CONCLUSIONS: The application of the win ratio methodology to the MERINO trial data illustrates its utility and feasibility for use in antimicrobial trials.