Trial shows using two drugs not better than one when treating MRSA blood infections

Researchers attempting to improve the treatment for methicillin-resistant Staphylococcus aureus (MRSA) blood infections have discovered the combination of two antibiotics was no better than one, and led to more adverse effects.

Staphylococcus aureus bacterial colonies

MRSA bloodstream infections have a mortality rate between 20 and 25 per cent and cause around 1000 infections a year in Australia.

To test combination antibiotic treatment, the largest trial of MRSA bloodstream infections to date (352 participants from Australia, Singapore, New Zealand and Israel) was established. The trial was called the CAMERA2Combination Antibiotic Therapy for Methicillin Resistant Staphylococcus Aureus infection.

In the CAMERA2 trial, researchers from the Menzies School of Health Research (Menzies) and the Doherty Institute were surprised to see the drug combination wasn’t as effective as anticipated.

“The current treatment for MRSA bloodstream infections is an old drug called vancomycin, but it doesn’t kill MRSA quickly. So, there is an urgent need to find new treatment solutions for this deadly infection,” says Professor Joshua Davis from Menzies.

“Many laboratory studies have shown that combining vancomycin with a penicillin-class antibiotic results in improved killing of MRSA.”

In this clinical trial involving patients from four countries, half of the participants were randomly allocated to receive vancomycin therapy and the other half received a combination of vancomycin and a penicillin-class antibiotic.

Published in the journal JAMA, results showed that although the MRSA was killed more quickly, this did not translate to fewer deaths. Surprisingly, combination treatment led to more episodes of kidney injury.

One of the lead researchers, a Royal Melbourne Hospital Clinician Researcher and co-lead of Clinical Translational Research at the Doherty Institute, Associate Professor Steven Tong, says this was a significant finding for the future treatment of MRSA infections.

“Clinicians now have the latest evidence as to what works and what doesn’t when treating MRSA bloodstream infections, and this trial shows more is not better,” says Associate Professor Tong.

Professor Joshua Davis working on microscope
Associate Professor Steve Tong

This work will now continue with a National Health and Medical Research Council (NHMRC) $5 million grant to conduct the Staphylococcus aureus Network Adaptive Platform trial (SNAP).

“Golden staph is a bacterium that causes over 5000 bloodstream infections a year in Australia, with a mortality rate of 20 per cent, and yet despite these numbers, there is little evidence to guide best management,” explains Associative Professor Tong.

“This grant brings together a global collaboration to conduct the largest ever clinical trial for Staphylococcus aureus bloodstream infections and address common questions around how to best treat these infections for patients all over the world.”

This work is supported by the NHMRC.

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