For people with advanced HIV infections, a new drug seems to suppress the virus better than existing treatments.

Antiviral drugs called protease inhibitors have been the gold standard for treating HIV since the mid-1990s, but the virus is becoming increasingly resistant.

The new drug, darunavir, also called Prezista, is like other protease inhibitors. This class of drugs is designed to lock up an enzyme that the virus needs to make copies that can infect cells.  

In a new study, researchers looked at 100 people who took darunavir in combination with a low dose of an older protease inhibitor called ritonavir, and a control group of 120 people who took an existing combination therapy.

People in both groups had advanced HIV infection and their current therapies were failing, said Dr. Bonaventura Clotet of Barcelona and colleagues in Thursday's online issue of the medical journal the Lancet.

About 45 per cent of those taking darunavir-ritonavir showed the lowest recordable level of HIV genetic material in their blood compared to 10 per cent in the control group.

People taking darunavir-ritonavir also showed an increase in the immune system's CD4 cells that was five times higher than among those in the other group (19 cells per microlitre versus 102 cells per microlitre).

Doctors use the amount of HIV in the blood, or viral load, and the levels of infection-fighting CD4 cells to track progression to AIDS and to measure if antiretroviral therapy is working.

New option for HIV resistance

To prove darunavir works, patients will need to be tracked, ideally for another two or three years, Dr. Rodger MacArthur of Wayne State University in Detroit said in a journal commentary.

"For now, all of us treating HIV-infected individuals in clinical practice will probably rejoice in the availability of darunavir, since it seems to be a safe, well-tolerated, and truly effective agent against multi-drug resistant HIV," MacArthur wrote.

Darunavir-ritonavir also needs to be compared to an existing therapy, tipranavir-ritonavir, since resistance to one could fuel resistance to the other.

The virus mutates quickly and may resist medications, especially if drug regimens are not followed closely.

Failure rates for antiretroviral drugs range from 21 per cent among patients already taking the medications, to 11 per cent in those just starting treatment, the researchers said.

Prezista is approved for sale by the U.S. Food and Drug Administration, and with conditions by Health Canada and European regulators.

At the International AIDS Conference in Toronto in 2006, researchers reported early results of a new class of drugs, called integrase inhibitors, that stop the genetic material's ability to integrate with the host chromosome.