The TB bacterium can become resistant to drugs

The antibiotic, linezolid, saved four women and a child in the US who were all seriously ill with drug-resistant TB.

Doctors treating the patients, who were aged between ten and 54, tried between eight and 14 drugs on each patient without success before using the linezolid.

TB can usually be cured with a six-month course of antibiotics.

The important factors in treating multi-drug resistant TB are that the drugs are cheap and that you never use a single drug alone Paul Sommerfeld, TB Alert

But patients with drug-resistant strains can need up to two years' of treatment with powerful drugs to cure their TB.

Drug-resistant strains of TB develop when patients do not finish their course of treatment or are given the wrong combination of drugs.

It is a particular problem in parts of Eastern Europe.

Until now, researchers had been unable to find any drugs which could be used to fight the new strains.

'Desperation'

Researchers from the New York University School of Medicine considered linezolid (Zyvox) after laboratory tests showed it had been effective in the treatment of TB.

It has been licensed by the US Food and Drug Administration to treat other bacteria which are resistant to standard antibiotics such as penicillin and methicillin, but has not approved to treat drug-resistant TB.

The researchers gave linezolid twice a day for between nine to 33 months.

Following the treatment, no patients showed any symptoms of TB, and no severe side effects were seen.

William Rom, professor of medicine and environmental medicine at NYU School of Medicine, said: "This group of patients were our most difficult to treat. They were in a lot of trouble, and we had run out of treatment options."

Dr Timothy Harkin, director of chest services at Bellevue Hospital, who worked on the study, said: "Trying the linezolid was a real act of desperation.

"This certainly seems like a promising medication for multidrug-resistant TB and there is a continuing need for new antibiotics for this disease."

The researchers say larger studies are needed to confirm their findings.

Single drug

Paul Sommerfeld, chair of the UK group TB Alert, told BBC News Online: "This study is interesting.

"But the important factors in treating multi-drug resistant TB are that the drugs are cheap and that you never use a single drug alone.

"If you just use a single drug, resistance against it will soon build up."

TB kills around two million people each year, and around eight million new cases are diagnosed.

More than a third of the world's population is infected with the TB bacterium.