AIDSWEEKLY Plus; Monday, April 16, 2007
Staff Medical Writers

There is an urgent need for new antiretroviral drugs due to rates of failure in existing combination antiretroviral therapies. Rates of failure after six years are currently 21 per cent for treatment experienced patients and 11 per cent for those new to treatment.

The current study looked at the effectiveness of the new 'protease-inhibitor' darunavir, when used in conjunction with a boosting (low) dose of the existing antiretroviral drug ritonavir.

Patients in the control group were given an existing background combination therapy while others were given the background drugs plus darunavir-ritonavir twice daily. Both groups had advanced HIV infection and their existing combination therapies were failing.

Darunavir-ritonavir substantially outperformed the control group both virologically and immunologically.

Dr Bonaventura Clotet of the Hospital Universitari Germans Trias i Pujol, Barcelona, Catalonia, Spain, and colleagues measured the amount of HIV genetic material (HIV RNA) in the blood of patients after 48 weeks, and found that 61 per cent of those taking the new drug achieved a ten fold drop in the amount of HIV RNA – the target of the study. Just 15 per cent of the control group reached this target.

Almost half (45 per cent) of those taking darunavir-ritonavir reduced their HIV RNA concentrations to below 50 copies per ml of blood – the lowest recordable value - while only 10 per cent of the control group achieved this.

Equally encouraging were the effects of the drug on the immune system, namely the boosting effect on the number of CD4 cells which form the immune response. This is often judged a better predictor of disease progression than HIV RNA concentrations.

The number of CD4 cells in patients taking the new drug combination increased by an average of 102 cells per microlitre, compared to just a 19 cells per microlitre increase in the control group.

Previous studies have shown that less than 10 per cent of patients on regular combination therapy whose CD4 count increases by more than 100 cells per microlitre progressed to AIDS or died within three years – compared with 85 per cent of those with a CD4 count increase of less than 25 cells per microlitre. These data further support the significant favourable impact that darunavir therapy might achieve in an advanced patient population with low CD4 counts.

Dr Rodger MacArthur, of Wayne State University, Detroit, Michigan, says in an accompanying comment that clinical endpoint studies – ideally two to three years later – would be needed to fully establish the efficacy of darunavir. A comparison of darunavir-ritonavir with tipranavir-ritonavir (an existing therapy) would also be needed, as some cross resistance can occur between the two drugs.

But he added: "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."

Keywords: HIV/AIDS, AIDS, Acquired Immunodeficiency Syndrome, Antivirals, Biotechnology, Clinical Trial Research, Combination Therapy, Drug Development, HIV, Human Immunodeficiency Virus, Protease Inhibitor, Treatment, Virology, Hospital Universitari Germans Trias i Pujol.

This article was prepared by AIDS Weekly editors from staff and other reports.

Reference

Clotet B, Bellos N, Molina JM, et al., Efficacy and safety of darunavir-ritonavir at week 48 in treatment-experienced patients with HIV-1 infection in POWER 1 and 2: a pooled subgroup analysis of data from two randomised trials., Lancet. 2007 Apr 7;369(9568):1169-78..

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2007-04-16
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