Merck & Co has reported encouraging interim 24-week data from an ongoing Phase II dose-ranging study with MK-0518, its twice-daily, investigational oral HIV integrase inhibitor, at the 16th International AIDS Conference, held in Toronto, Canada.

According to Merck, the combination of MK-0518 with Gilead Sciences' Viread (tenofovir) and GlaxoSmithKline's Epivir (lamivudine) showed viral load reduction to undetectable levels (below 50 copies/mL of HIV RNA) at least as good as a triple-drug combination of Bristol-Myers Squibb's Sustiva (efavirenz), Viread and Epivir, commonly used as a starting regimen in newly-diagnosed HIV patients.

Merck’s drug achieved this endpoint in 85%-95% of patients, depending on the dose, while with the Sustiva regimen this occurred in 92% of patients. MK-0518 tended to achieve undetectable levels faster than the rival regimen, according to Merck’s director of clinical research Robin Isaacs.

Meanwhile, GlaxoSmithKline and partner Shionogi said they had completed an initial clinical study with another integrase inhibitor, 364735, and would present the Phase I data at a meeting next year. The companies now intend to start a Phase II programme for the compound later this year.

Integrase is one of the three enzymes necessary for HIV to replicate in the body, and integrase inhibitors would stop HIV from inserting its genes into uninfected DNA. The other two enzymes necessary for viral replication, reverse transcriptase and HIV protease, already are targeted by a variety of antiretroviral drugs.