Combining Trimeris and Roche’s HIV drug Fuzeon with another antiretroviral developed by Merck & Co creates a regimen with unprecedented efficacy in reducing circulating levels of the virus in the blood, according to new data.

Fuzeon (enfuvirtide), n HIV fusion inhibitor was given alongside Merck’s experimental integrase inhibitor MK-0518 and drove HIV levels in the blood below the limits of detection in 90% to 95% of patients tested, according to the Phase II study.

The results were made all the more exceptional by the fact that patients enrolled into the trial had all been extensively treated with other drugs and harboured resistant strains of HIV, said Roche.

Merck reported data from another Phase II trial in the summer indicating that MK-0518 also worked well as part of a triple regimen including Gilead Sciences' Viread (tenofovir) and GlaxoSmithKline's Epivir (lamivudine). In this study, 85% to 95% of patients achieved undetectable levels of the virus.

In the latest study, patients received one of three doses of MK-0518 (200mg, 400mg or 600mg) twice-daily in combination with an optimised background regimen of anti-HIV drugs. In the subset of patients who received Fuzeon for the first time in their drug regimen, 90% to 95% achieved undetectable HIV, compared to 60% to 70% of subjects who received MK-0518 with Fuzeon.

The results were presented at the Intersciences Conference on Antimicrobial Agents and Chemotherapy in San Francisco, USA, yesterday.