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ISSUE 2149 Friday 13 April 2001

New drug losing battle against hospital superbug

By David Derbyshire, Medical Correspondent

A "WONDER DRUG" recently introduced to tackle antibiotic resistant superbugs is already losing its effectiveness against bacteria.

Research published today says some strains of hospital bacteria are developing resistance to linezolid and might become untreatable. Linezolid is one of a new class of antiobiotics designed to kill bacteria resistant to conventional antibiotics. These superbugs include methicillin resistant Staphyloccus aureus (MRSA) and vancomycin resistant enterococcus (VRE).

The drug is available in Britain and is used to treat some of the 100,000 people who pick up infections in hospital each year. Dr Ronald Gonzales of the University of Illinois College of Medicine studied the use of linezolid against a vancomycin resistant superbug called enterococcus faecium. Vancomycin was once regarded as the last line of defence against superbugs.

Linezolid was initially effective in all five patients. But over several weeks, tests showed that bacteria were beginning to develop resistance. In three cases, the patients grew unresponsive to treatment, the team reports in the Lancet today. Four of the patients had been given transplants and all were on long courses of the drug, between 21 and 40 days. That increased the chances of the bacteria becoming resistant, the team reports.

"Resistance may emerge during linezolid therapy for VRE infections, especially during long courses, and may be associated with treatment failure," they write. They called for doctors to test for resistance at the start of treatment.

But public health experts yesterday stressed that the drug would still be effective for many patients, and that there was no reported resistance from MRSA. Simon Gregor, of the Public Health Laboratory Service, said enterococci were genetically more likely to develop resistance than MRSA.

He said: "The fact that resistance is found with enterococci doesn't mean that it will be found in other organisms. It is less likely that resistance will evolve in MRSA and if it does, it is likely to be a much slower process. An inevitable consequence of developing these new antibiotics is that eventually the bacteria will build up resistance to them. Developing new drugs like this is only part of the issue. What we need to be looking at is preventing infections in the first place."

Linezolid, made by Pharmacia and Upjohn, is one of a new class of antibiotics called oxazolidinones. These were the first new antibiotics for 20 years. It is effective against MRSA and other gram positive bacteria resistant to powerful antibiotics such as vancomycin, trovafloxacin and teicoplanin.

Traditional antibiotics work by dissolving or preventing the building of the cell wall, tampering with the genetic material of bacteria to stop them reproducing or by preventing the organisms from making or using certain proteins.

Linezolid works by sabotaging a bacterium's ribosomes and RNA messenger for DNA, both of which are involved in assembling proteins. In order for it to become resistant, several genes have to change at once.

-- Anonymous, April 12, 2001