Merck reported positive results from an ongoing phase II trial of Isentress for the treatment of HIV. This multi-center, dose-ranging, double-blind, randomized trial enrolled 198 treatment-naïve HIV-infected subjects.

The subjects received Isentress administered orally twice daily in combination with tenofovir and lamivudine or 600 mg efavirenz, dosed orally once daily in combination with the same agents.

During the first 48 weeks of the study, four dose regimens of Isentress (100, 200, 400 and 600 mg) were studied. After 48 weeks, all Isentress groups received 400 mg dosed twice daily. The primary endpoints were reductions in HIV RNA less than 400 copies/mL and the evaluation of safety at 96 weeks.

At baseline mean HIV, RNA for subjects on the Isentress combined regimen was approximately 55,000 copies/mL and for the efavirenz regimen was approximately 68,000 copies/mL. Mean baseline CD4 cell counts were 305 and 280 cells/mm³ for the groups receiving Isentress and efavirenz, respectively.

Following 96 weeks of treatment the Isentress combination therapy reduced HIV viral load to undetectable levels, with 83% of subjects achieving reductions in HIV RNA levels below 50 copies/mL. These results were comparable for subjects in the efavirenz treatment arm, with 84% of subjects achieving reductions in HIV RNA levels below 50 copies/mL.Similarly, 84% of subjects in both treatment arms maintained reductions in HIV RNA levels to below 400 copies/mL.

In addition, subjects on both treatment regimens experienced increases in CD4 cell counts at 96 weeks. The mean increase from baseline in CD4 cell count was 221 cells/mm3 for subjects taking Isentress and 232 cells/mm³ for those taking efavirenz.

Treatment was generally safe and well tolerated. Based on the results, Merck plans to move forward with the development of Isentress for this treatment-naïve population.