Cefazolin Matches Antistaphylococcal Penicillins on Survival in MSSA Bacteremia

A 1,303-patient Bayesian platform trial settles four decades of clinical debate: the cheaper, more forgiving beta-lactam performs as well as the guideline gold standard on 90-day mortality — and comes with a kidney-sparing advantage.

Clinical Trials Desk Saturday, 20 June 2026 · 2 min read

For four decades, clinicians treating Staphylococcus aureus bacteremia faced a question without a rigorous randomized answer: could cefazolin — cheaper, easier to administer, and anecdotally more renal-sparing than the guideline-preferred antistaphylococcal penicillins (ASP) — substitute for nafcillin, oxacillin, or flucloxacillin? The SNAP trial, reported this week in the New England Journal of Medicine, has now produced the most definitive evidence yet: on survival, cefazolin does not lose.

Trial Design and Enrollment

SNAP (Staphylococcal Bacteremia Antibiotic Treatment Platform) enrolled 1,303 adults with confirmed methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia at centers across the United States, Canada, and Australia, using an adaptive Bayesian platform design that allowed continuous learning and pre-specified interim decisions. Participants were randomized to cefazolin 2 g intravenously every eight hours or to an ASP — nafcillin, oxacillin, or flucloxacillin at investigator’s choice — for a minimum of 14 days, with duration adjusted for source and clinical response.

The primary endpoint was 90-day all-cause mortality. A key secondary endpoint was acute kidney injury (AKI) within 14 days, defined by KDIGO criteria.

What the Data Showed

Ninety-day mortality was 15.0% with cefazolin versus 17.0% with ASP. The adjusted odds ratio of 0.81 (95% credible interval 0.59–1.12) satisfied the pre-specified Bayesian noninferiority criterion; the posterior probability that cefazolin was noninferior exceeded the trial’s threshold.

The kidney signal was not subtle. AKI at 14 days occurred in 13.9% of cefazolin recipients versus 19.6% in the ASP group (aOR 0.67, 95% CrI 0.50–0.89) — a 32% relative reduction in early nephrotoxicity.

The AKI advantage is clinically meaningful because bacteremia patients frequently accumulate concurrent nephrotoxic exposures: empiric vancomycin while cultures are pending, iodinated contrast for source-control imaging, and vasopressors in septic shock. Replacing the antistaphylococcal penicillin with cefazolin removes one layer of that stacked renal hazard.

Caveats and Scope

SNAP was not designed as a superiority trial. The mortality credible interval includes values modestly favoring ASP, and noninferiority does not establish that cefazolin is better on survival — only that it is not meaningfully worse. The trial enrolled predominantly catheter-related bacteremia; patients with endocarditis, particularly prosthetic-valve or device-associated infection, were managed with individualized therapy and are incompletely represented in the randomized cohort. Whether the survival equivalence extends to CNS seeding or complicated left-sided endocarditis requires further study.

Notwithstanding those limits, SNAP represents the largest randomized comparison of cefazolin versus ASP in MSSA bacteremia by a substantial margin. The platform design’s Bayesian framework also sets a precedent: future arms can be added without starting a new trial, enabling the research community to build cumulative evidence for additional management questions in this common and lethal infection.

SNAP Investigators. Cefazolin versus antistaphylococcal penicillins for MSSA bacteremia. N Engl J Med. 2026;394:2329–2339. DOI: 10.1056/NEJMoa2602847.

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90-day all-cause mortality was 15.0% with cefazolin versus 17.0% with antistaphylococcal penicillins (aOR 0.81, 95% CrI 0.59–1.12), satisfying the pre-specified Bayesian noninferiority criterion.

source on file

Acute kidney injury at 14 days occurred in 13.9% of cefazolin recipients versus 19.6% in the ASP group (aOR 0.67, 95% CrI 0.50–0.89).

source on file

SNAP enrolled 1,303 adults with MSSA bacteremia in an adaptive Bayesian platform trial.

source on file

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