SNAP trial shows safer antibiotic option for staph blood infection

18 Jun 2026

A landmark international clinical trial, led in the UK by Professor Anna Goodman at our Unit, has identified the optimal antibiotics for staph blood infection, a breakthrough that is set to reshape treatment for the life-threatening condition.

The SNAP trial found that a little used antibiotic, cefazolin, is as effective as and safer than the current UK standard therapy, flucloxacillin, for treating life-threatening staph blood infections.

The researchers also found that a commonly used antibiotic, penicillin, can be used when the staph is treatable with this in the laboratory. And that similarly, this is probably as effective as flucloxacillin, and safer.

The findings from the SNAP Trial, published in the New England Journal of Medicine (NEJM) and The Lancet, challenge the long-held assumption that flucloxacillin should remain the default treatment and provide important new evidence to guide treatment strategy.

Staph (Staphylococcus aureus) is a leading cause of deadly blood infection, associated with over 1 million deaths worldwide each year and affecting over 14,000 patients each year in the UK. While effective antibiotic treatments exist, there has been no clear agreement about which antibiotic leads to the best outcomes for patients.

The NEJM results – Comparing cefazolin and flucloxacillin

In the trial published in the NEJM, researchers compared antibiotics used to treat meticillin-susceptible (i.e. not resistant to meticillin) Staphylococcus aureus (MSSA) infections. It found cefazolin is at least as good as flucloxacillin for helping people to survive this infection, and associated with fewer side effects and a lower risk of kidney injury. It compared cefazolin and flucloxacillin in 1,341 adults with staph blood infections across eight countries taking part in this part of the trial.

In patients who received cefazolin there were fewer cases of changes in how the kidneys are working (as measured by blood tests). Such kidney changes can cause long-term health problems and occurred in fewer of those given cefazolin compared to those given flucloxacillin.

The Lancet results – Comparing benzylpenicillin and flucloxacillin

In the paper published in The Lancet, the trial evaluated whether penicillin could be used to treat penicillin-susceptible Staphylococcus aureus (PSSA) infections where laboratory testing confirmed the susceptibility to penicillin.

This trial compared penicillin and flucloxacillin in 281 adults with staph blood infections. Penicillin was found likely to be at least as good for helping people to live with this infection as flucloxacillin.

In patients who received penicillin there were similarly fewer cases of changes in how the kidneys are working (as measured by blood tests). These occurred in 11 per cent of those given penicillin compared to 22% of those given flucloxacillin. Mortality was also 14% in the penicillin group compared with 22% in the flucloxacillin group.

Staph infections are caused by bacteria called Staphylococcus aureus. They most often affect the skin and cause relatively minor problems. However, if the bacteria enter the bloodstream or other parts of the body, they can cause serious infections such as blood poisoning, blood infection or sepsis.

These more serious infections can affect anyone, but individuals at higher risk include people with catheters in their veins (as happens when people receive renal replacement therapy also called haemodialysis) or implanted devices (such as pacemakers), and people with diabetes. Those living with cancer and on immune-suppressing medication, those who cannot get out of bed, and those who inject drugs are also more vulnerable to these infections.

A shift away from flucloxacillin

Researchers said these results mark a turning point in the treatment of MSSA and PSSA blood infections, signalling a shift in clinical practice.

Penicillin was once widely used to treat Staphylococcus aureus, but antibiotic resistance of staph led clinicians to adopt flucloxacillin as the standard treatment for MSSA and PSSA blood infections. The findings support moving away from flucloxacillin as the default treatment for MSSA and PSSA blood infections, given safer alternatives are available.

The new results mark the first major finding from the ongoing SNAP trial, which aims to improve treatment for Staphylococcus aureus infections around the world. These parts of the trial took place in Australia, Canada, Israel, the Netherlands, New Zealand, Singapore, South Africa and the UK – each supported by regional funders working together to form one global network.

So far, over 6,000 participants have been enrolled in over 150 sites in those countries stated, and more recently in France, Germany, Sweden, Japan, Malaysia, and the United States. The trial will continue testing new approaches to improve outcomes for patients facing this serious infection.

Translating the findings

Researchers say the next challenge will be translating the findings into routine clinical practice.

While cefazolin availability may need to increase in some countries, researchers say implementation will ultimately depend on hospitals, laboratories and guideline groups incorporating the findings into clinical care.

In the UK, SNAP was funded by the National Institute for Health and Care Research (NIHR133719). Additional funds were provided from the Medical Research Council (MC_UU_0004/05).

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