Fuzeon (enfuvirtide), the first and only fusion inhibitor for the treatment of HIV, durably suppresses HIV and provides continuous increases in immune (CD4) cells over a period of 96 weeks, according to new data presented at the XV International AIDS Conference (IAC). In another key study finding, more than half of treatment-experienced patients (56 per cent) who began using Fuzeon at the outset of the study were successful in completing 96 weeks of treatment. Additionally, investigators reported no late-emerging safety issues associated with the long-term use of Fuzeon.

"The new data show that the significant virological and immunological benefits of Fuzeon seen in earlier analyses are extended to 96 weeks, an especially notable achievement given the extensive prior drug exposure of patients enrolled in the TORO studies," said Corklin Steinhart, senior attending physician, Mercy Hospital, Miami, FL. "It is particularly exciting that more than half of patients who began treatment with Fuzeon continued on the drug for 96 weeks. This news, coupled with the positive 96-week safety analysis, should be encouraging to patients who are considering Fuzeon as a long-term treatment option," he added.

The high prevalence of HIV drug resistance among patients in the US highlights the need for newer HIV drugs, like Fuzeon, that are active against drug-resistant virus. Data recently presented at the XII International Drug Resistance Workshop, from a large cohort of HIV-infected individuals prescribed antiretroviral therapy from 2001-2003, showed that four out of five of those tested had resistance to at least one anti-HIV drug. Thirty-nine per cent were found to have resistance to a drug in two classes, and 18 percent had resistance to a drug in three classes. These data are consistent with previous findings from a different study recently published in AIDS by Dr. Douglas Richman, which showed that 76 per cent of US patients with measurable viral load in 1996-1998 carried a strain of the virus that is resistant to at least one drug.

The data presented at IAC were from a 96-week analysis of the TORO studies, two randomized, open-label trials that together enrolled approximately 1,000 HIV infected patients who had previously been treated with an average of 12 antiretrovirals. Patients were randomized to receive a regimen of anti-HIV drugs with or without Fuzeon. Patients randomized not to receive Fuzeon were allowed to add Fuzeon to their regimens after week eight if they met virological failure criteria or at the 48-week timepoint.

Patients who were randomized to receive a Fuzeon-based regimen had significantly lower levels of the virus and higher CD4 counts at 96 weeks compared with those randomized to a regimen without Fuzeon. Patients originally in the non-Fuzeon control arm who were later switched to Fuzeon (after virological failure) showed a mean reduction in viral load at week 96 of 1.1 log10 copies/mL, compared to a 2.1 log10 copies/mL mean reduction for patients randomized to the Fuzeon arm - thereby highlighting the potential consequences of delaying the initiation of treatment with Fuzeon.

Patients in the Fuzeon arm saw continuous improvements in CD4 cells over the study period, with the mean CD4 increase from baseline of 166 cells/mm3 at week 96. In contrast, patients who used Fuzeon after switching from a non-Fuzeon regimen, experienced a mean increase of 116 cells/mm3 from baseline at week 96.