A study led by Sydney researchers has found that the treatment, called raltegravir, worked ''extremely well'' for more than half of all patients with long-standing, drug-resistance to the disease.

The drug, the first in a new class of anti-retrovirals called integrase inhibitors, is being heralded as a breakthrough in HIV treatment.

HIV specialist Professor David Cooper, from the National Centre in HIV Epidemiology and Clinical Research at the University of NSW, said, ''It has the potential for changing the treatment landscape.

''It is getting results in patients who had stopped responding to other drugs and were getting sicker, so this is very important.''

About 500 Australian patients who were failing on their current treatments were involved in a drug company-funded international trial.

The results, published in the journal The Lancet yesterday, showed that raltegravir lowered the amount of virus in the blood to undetectable levels in 62per cent of people taking it in combination with other medicines. AAP