A new drug for HIV sufferers is being launched in the UK today.
Studies show that 75 per cent of patients receiving the drug raltegravir have a reduction in HIV viral load in their blood, compared with 40 per cent taking a dummy drug.
The groups were taking raltegravir or the dummy pill in combination with other therapies.
Raltegravir is for patients who have failed on other treatments and works by blocking an enzyme essential for HIV to replicate itself.
Its effectiveness is noted by its ability to drive down levels of HIV genetic material (RNA) in the blood.
Raltegravir is the first in a new class of HIV treatments called integrase inhibitors.
Scientists hope this new family of drugs will get round the problem of treatment-resistant HIV strains.
Dr Mark Nelson, director of HIV services at London's Chelsea and Westminster Hospital, said it could provide a lifeline for patients failing on existing treatments.
"For these people, the emergence of new classes of drugs such as integrase inhibitors will offer new hope," he added.
During the trials, patients were taking raltegravir or the dummy drug plus Optimised Background Therapy (OBT).
OBT is a regime of antiretroviral drugs tailored to individual patients.
One study published in The Lancet medical journal in April 2007 was based on 178 patients with advanced HIV.
They had been taking regular antiretroviral HIV drugs for about 10 years but were failing to respond to them.
Researchers measured the amount of viral load - or HIV RNA - in their blood after 24 weeks of treatment with their usual HIV drugs plus either raltegravir or a dummy drug.
Patients taking raltegravir had an average of 98 per cent drop in their HIV RNA count, compared with 45 per cent drop in the dummy drug group.
The number of CD4 cells, an indicator of the immune response, was also boosted in patients taking raltegravir.
A recent report from the National Aids Trust showed that more than a quarter of Britons did not know that HIV could be caught as a result of unprotected sex between two men. In 2000, the figure was just 12 per cent.
Over a fifth were also not aware that HIV could be spread by sex between men and women, compared with 9 per cent in 2000.