Spanish scientists researching two POWER studies presented at the International AIDS Conference last year in Toronto said Thursday in Barcelona the third-generation protease inhibitor darunavir (Prezista) is highly effective in combating highly resistant HIV. (File Photo)

    BEIJING, April 6 (Xinhuanet) -- Spanish scientists researching two POWER studies presented at the International AIDS Conference last year in Toronto said Thursday in Barcelona the third-generation protease inhibitor darunavir (Prezista) is highly effective in combating highly resistant HIV.

    In two parallel phase IIB randomized trials, darunavir, augmented by the protease inhibitor ritonavir, was better at reducing viral load than control drugs, said Bonaventura Clotet, M.D., of the Hospital Universitari Germans Trias i Pujol.

    After 48 weeks, 67 of 110 (61 percent) of darunavir patients had seen their viral load drop by a factor of 10, compared with 18 of 120 (15 percent) of patients getting control protease inhibitors, Clotet and colleagues reported online in The Lancet. The difference in response was 46 percent, which was significant at P<0.0001.

    On the basis of a logistic regression model including stratification factors (baseline number of primary protease inhibitor mutations, use of enfuvirtide, baseline viral load) as covariates, the difference in response was 50 percent.

    Patients in the darunavir group also had a significantly greater chance of having a viral load of less than 50 copies of viral RNA per cubic milliliter of blood -- the lower limit of detectability.

    That finding underscores the possibility of reaching such a low HIV level, even in patients whose virus is resistant to multiple drugs, Clotet and colleagues said.

    The target is a "stringent yet realistic therapeutic goal" whose benefit is that it may delay or prevent the emergence of resistance, they said.

    The finding comes from the two POWER studies, which began with 24 weeks of dose-finding and primary efficacy analyses. At 24 weeks, the researchers settled on a twice-daily dose of 600 mg of darunavir and 100 mg of ritonavir and patients getting other doses were switched.

    For this 48-week analysis, only patients who had been on the twice-daily 600/100 dose from the beginning were included. They were compared with patients in the control arm -- getting an optimized background regimen, including a protease inhibitor - who simply continued on this therapy.

    The study was sponsored by Tibotec Pharmaceuticals Ltd. Clotet reports receiving consulting and lecture fees from Gilead, Roche, Bristol Myers Squibb, GlaxoSmithKline, Tibotec, Boehringer Ingelheim, Pfizer, and Abbott. Other authors report similar ties to, as well as research support from, GlaxoSmithKline, Roche, Bristol Myers Squibb, Gilead, Pfizer, Tibotec, Johnson & Johnson Monogram Bio, Tanox, Virco, and Sequoia Pharmaceuticals.

    Two of the authors, Sabrina Spinosa-Guzman, M.D., and Eric Lefebvre, M.D., are full-time employees of Tibotec.

    (Agencies)