Merck's MK-0518 reduces viral load during phase 2 HIV study

By Angela McDaniels

Seattle, Feb. 9 - Merck & Co. Inc. said interim results from a phase 2 trial of MK-0518 showed that the oral investigational medication in combination with optimized background therapy provided greater viral suppression than a placebo with optimized background therapy.

In the multi-center, double-blinded, phase 2 study, 167 patients with advanced HIV infection who were failing anti-retroviral therapy were randomized to receive 200 mg, 400 mg, 600 mg or a placebo orally twice a day in combination with optimized background therapy.

Optimized background therapy was selected based on the patient's prior treatment history and results from HIV resistance testing, the company said. Each patient had viruses resistant to at least one drug in each of the three available classes of oral anti-retroviral therapy: nucleoside reverse transcriptase inhibitors, non-nucleoside reverse transcriptase inhibitors and protease inhibitors.

After 16 weeks, 64% to 84% of patients treated with MK-0518 had HIV RNA levels of less than 400 copies per mL, compared with 5,000 when the study began. Of the placebo group, the percentage was 22%, according to a company news release.

In addition, 56% to 72% of patients had HIV RNA of less than 50 copies/mL, compared with 19% for the placebo group.

Merck said the regimen of MK-0518 plus optimized background therapy was generally well tolerated and comparable to the regimen of a placebo plus optimized background therapy.

The most commonly reported study therapy-related side effects were diarrhea, nausea, fatigue, injection-site reaction, headache and itching.

The results were presented on Wednesday at the 13th Annual Conference on Retroviruses and Opportunistic Infections in Denver.

MK-0518 is an integrase inhibitor that prevents the insertion of the HIV viral DNA into the human DNA genome. Inhibiting integrase from performing this essential function blocks the ability of the virus to replicate and infect new cells, according to the release.

Merck is a pharmaceutical company based in Whitehouse Station, N.J., that develops vaccines and pharmaceuticals.

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