July 17, 2003

Ed Susman

July 17, 2003 (Paris) — Enfuvirtide, the first approved fusion inhibitor, maintains its ability to suppress HIV for at least a year, according to a presentation here yesterday at the Second International AIDS Society Conference on HIV Pathogenesis and Treatment. Enfuvirtide is also known as T-20.

After one year, 37.2% of patients taking enfuvirtide had achieved a more than 90% (one log) reduction in viral load compared with 17.1% patients who received an "optimized background" regimen of conventional antiretroviral drugs, said David Cooper, MD, professor of medicine at the University of New South Wales, and director of the National Centre in HIV Epidemiology and Clinical Research in Sydney, Australia. These results come from studies of enfuvirtide in patients with extensive prior treatment and resistance to other antiretroviral drugs.

Previously, after 24 weeks of treatment, the researchers had reported that 47.2% of patients receiving enfuvirtide had achieved a greater than one log reduction in viral load compared with 24.9% of patients receiving background medication only, and 32.7% of enfuvirtide-treated patients had achieved undetectable viral load levels compared with 15% of those not receiving the study drug. At 48 weeks, 30% of enfuvirtide-treated patients continued to have undetectable viral load levels compared with 12% of those receiving background medication. The differences, he said, were statistically significant ( P < .001).

In the TORO studies, patients were randomized in an open-label fashion on a 2:1 basis to receive either 90 µg of enfuvirtide by subcutaneous injection twice daily in addition to the best available HIV treatment. The international studies — TORO 1 in North and South America and TORO 2 in Europe and Australia — enrolled 995 patients. All of the patients in the study had been previously treated with numerous antiretroviral drugs in all three conventional drug classes. "The median number of antiretroviral drugs used was 12 among these patients," Dr. Cooper said. "They had been treated an average of seven years with antiretrovirals."

"T-20 appears to be more durable than some of us would have believed," said Mark Wainberg, PhD, director of the McGill University AIDS Centre in Montreal, Quebec, Canada.

Robert Murphy, MD, clinical professor of infectious diseases at Northwestern University School of Medicine in Chicago, Illinois, said that the durability of enfuvirtide came as a bit of surprise to researchers. "However, I don't see the drug being used other than as a second-line or salvage therapy because of its mode of administration."

However, Dr. Wainberg said that an oral form of the drug is in development and its success could push the drug into first-line status because the TORO studies have shown it has long-lasting efficacy.

Second IAS Conference. Presented July 16, 2003.

Reviewed by Gary D. Vogin, MD

Ed Susman is a freelance writer for Medscape.

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