A drug recently listed on the PBS looks promising as part of a combination therapy with existing medicines for people with drug-resistant HIV.

New research from Professor David Cooper, director of the University of NSW's National Centre in HIV Epidemiology and Clinical Research (NCHECR) shows that raltegravir, marketed by Merck, effectively lowers virus load in blood to undetectable levels in 62 per cent of people taking it in combination with other anti-HIV drugs.

Only one in three people who received a placebo along with the other antiretrovirals had similar reductions. Results were based on analyses of viral load reductions and CD4 cell counts.

Raltegravir is an integrase inhibitor, which blocks the integrase enzyme from integrating the virus's genetic material into the target cell.

"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," Cooper said.

"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."

The research was published in the New England Journal of Medicine yesterday.