New antibiotics to fight `superbugs'

THE FIRST new class of antibiotics for 20 years is close to being licensed for use against "superbugs" that resist conventional drugs, say medical researchers.

The new drugs' mode of attack on bacteria should also make it less likely that resistant strains - such as those now leading to lethal infections in hospitals - will emerge.

Results unveiled over the weekend by members of the American Society of Microbiology showed that in trials involving 200 people, linezolid, a new antibiotic made by Pharmacia & Upjohn, cured 95 per cent of specific skin infections, and 96 per cent of cases of pneumonia, the bacterial infection of the lungs.

"It's worked pretty well," said Dr Robert Moellering of Harvard Medical School in Boston, Massachusetts, who has tested several new antibiotics in the laboratory.

The next step will be to apply for clearance from national bodies to license the drug, a process which could take more than a year.

However, the arrival of a new wave of antibiotics will be greeted with relief by doctors, who have seen dramatic rises in illnesses caused by bacteria that have become resistant to existing treatments, such as penicillin and vancomycin. More than 5,000 deaths are thought to be caused in the UK each year by MRSA, a strain of bacterium that is resistant to a wide range of antibiotics.

Linezolid is the first of a class of antibiotics known as oxazolidinones. "They represent a really unique class of antibiotics. There has been no unique antibacterial on the market in 20 years," said Dr Moellering.

Existing antibiotics kill bacteria by dissolving or preventing the building of the cell wall, or by stopping the bacteria from making or using essential proteins, or by interfering with their genetic material to prevent reproduction.

By contrast, linezolid sabotages two essential cell factors, the ribosomes, which assemble proteins, and RNA, the "messenger" for DNA, used to make the proteins essential for cell life.

More important to the long-term effectiveness of linezolid is that it affects processes stemming from several of the bacterial genes. That makes it less likely that resistance can evolve, because all the genes would have to change at once to produce a bacterium able to survive the antibiotic's effects.

Dr Moellering said Pharmacia did manage, with difficulty, to create bacteria in the laboratory that resisted linezolid, but none was seen in human patients.

"All of the data so far suggests that this is a drug for which it will be difficult for bacteria to become resistant, but we thought that was true for vancomycin, too," Dr Moellering said.

Vancomycin was seen as the last line of resistance against bacteria such as enterococci, which have developed resistant strains that defy all other known drugs. But hospitals in Japan and the United States have discovered vancomycin-resistant enterococci in patients with suppressed immune systems who have been on antibiotics for weeks.

The key to preventing linezolid and its kin falling by the wayside will be to prevent overuse, and to ensure that people complete courses so that all the bacteria are killed off, said Dr Moellering.