A drug to treat HIV infection offers new hope for millions of patients, according to cientists at the University of New South Wales (UNSW).

The researchers say the majority of patients who have not responded to traditional treatments have had good results from a new combination therapy involving raltegravir.

They say that clinical trials have shown that raltegravir - already available in Australia - is safe and effective and has minimal side-effects when used with other anti-HIV medicines.

Writing about their observations in the New England Journal of Medicine, the researchers have revealed that raltegravir lowers the amount of virus in the blood to undetectable levels in 62 per cent of people taking it in combination with other anti-HIV medicines.

Only one in three people who received a placebo plus other anti-HIV medicines had the amount of virus in the blood reduced to similar levels, they say.

"This is the first drug in a new class of antiretroviral drugs called integrase inhibitors. The drug has a different mechanism of action, is very potent, seems very safe and has helped patients who have a virus that is resistant to older drugs and classes," says Professor David Cooper AO, the Director of UNSW's National Centre in HIV Epidemiology and Clinical Research (NCHECR).

"It initially will be used in developed countries, but hopefully it will be made available at cheaper prices for patients in developing countries who are facing the same problems," Professor Cooper adds.