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Protease Inhibitor Lowers Viral Loads Among HIV-Positive People With Drug Resistance, Study Finds

April 5, 2007

The protease inhibitor darunavir, sold under the brand name Prezista by Johnson & Johnson subsidiary Tibotec Pharmaceuticals, has been found to effectively decrease HIV viral loads after 48 weeks of use among people who have developed drug resistance, according to a study published in the April 5 online edition of the Lancet, the Los Angeles Times reports (Chong, Los Angeles Times, 4/5). FDA in June 2006 gave accelerated approval to Tibotec's application for sale and marketing of Prezista for use by HIV-positive people who are resistant to first-line drugs. Protease inhibitors work by blocking the action of an enzyme that cuts HIV proteins into the shorter sections that the virus needs to create copies of itself. Phase II clinical trials of Prezista found that the drug is effective against drug-resistant HIV strains and that it lowered viral loads to undetectable levels among nearly half of trial participants (Kaiser Daily HIV/AIDS Report, 6/26/06). According to the Times, the Lancet study combined two Tibotec-funded international studies of the drug and looked at 230 HIV-positive people who had not responded to at least three different types of antiretroviral drugs. The study participants all were given a standard drug regimen that was chosen by their physicians. The goal of the trial was to reduce participants' viral loads by 10, a factor known to improve survival rates, the Times reports (Los Angeles Times, 4/5). The researchers followed 110 HIV-positive people who took Prezista in combination with ritonavir and 120 HIV-positive people who took other protease inhibitors for 11 months, Reuters reports. According to the study, 45% of the people taking Prezista experienced a reduction in viral loads to undetectable levels, compared with 10% of participants who received other drugs (Dunham, Reuters, 4/4). In addition, the study found that 20% of participants in a small subgroup of the study who previously had not responded to any antiretroviral had a reduction in viral loads to undetectable levels. According to the Times, there was "no significant difference" in side effects between people who took Prezista and those who took other antiretrovirals, although those taking Prezista had more herpes infections. The researchers plan to conduct further research to determine whether Prezista should be given to people newly diagnosed with HIV, the Times reports (Los Angeles Times, 4/5).

Bonaventura Clotet -- lead study author from the Hospital Universitari Germans Trias i Pujol in Barcelona, Spain -- said the efficacy of Prezista is "very unexpected and very impressive," adding that the researchers are "very excited by the findings of quite dramatic suppression in viral load." Rodger MacArthur of Wayne State University, who wrote a commentary that accompanied the study, said physicians treating HIV-positive people will welcome the study's findings (Reuters, 4/4). Steven Johnson, director of the HIV/AIDS Clinical Program at the University of Colorado, said the study results open new options to treat drug-resistant HIV (Los Angeles Times, 4/5).

Online An abstract of the study is available online.

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