Biotech firm



, as expected, reported Monday that patients taking its experimental drug, T-20, were able to drastically reduce the level of HIV in their systems.

Trimeris and partner, the Swiss drug firm


, are developing T-20 as a

new type of anti-HIV drug called a "fusion inhibitor" that works by preventing the virus from entering healthy cells. The results from two Phase III clinical trials were unveiled Monday at the XIV International AIDS Conference.

Because it works differently than existing AIDS drugs, Trimeris and Roche believe T-20 will be used to treat patients whose HIV and AIDS have grown resistant to current treatment options. Trimeris is expected to file for the drug's U.S. approval in the third quarter.

In the first study, 37% of patients treated with T-20 and two other drugs had undetectable levels of the virus in their systems after 24 weeks, compared to 16% of patients who received a standard AIDS drug cocktail. The study enrolled 491 patients who had been treated previously with an average of 12 antiretroviral drugs.

In the second study, conducted the same way, 28% of patients receiving T-20 had undetectable viral loads at 24 weeks, compared to 14% of patients who got the standard treatment.

"These results of these pivotal trials suggest that T-20 may play a significant role in addressing the challenges facing treatment-experienced patients," said Dr. James Thommes, medical director at Roche, in a statement.

Roche and Trimeris hope to get T-20 approved in the U.S. by the end of the year, or early next year, but the drug is one of the most complicated ever produced, which could force delays as the companies work out kinks in the manufacturing process. In addition, T-20 will be the first HIV drug taken by injection, and could cost twice, or even three times, the price of current drugs, which could slow or limit sales.

Trimeris closed Friday at $41.10 and was trading higher by $1.25 to $42.35 in early trading Monday.