Enfuvirtide Benefits Persist for at Least 2 Years

The TORO (T-20 versus Optimized Regimen Only) studies have been the primary sources of data on the new drug enfuvirtide (T-20, Fuzeon). Enfuvirtide -- the first and still the only available agent in the new, fourth class of antivirals called entry inhibitors -- is targeted for people who have triple-class experience and are no longer responding to their current regimen. The final 2-year data from the TORO studies were presented at the XV International AIDS Conference in Bangkok. First-year results have already been presented at previous conferences.

Due to their similar study designs, the results of the TORO 1 and TORO 2 studies have been combined. These studies enrolled triple-class experienced people who were ready to switch to a new regimen because they were experiencing incomplete viral suppression on their current regimen. The patients were switched to either a new "optimized" regimen (the control arm) or an optimized regimen that included enfuvirtide.

Patient viral load at baseline was just over 100,000 copies/mL, and the baseline CD4+ cell count was about 90 cells/mm3. Most of the participants had a prior AIDS-defining clinical illness. Those on the control arm who were not fully suppressed during the first year of the study, based on certain definitions of viral rebound or incomplete suppression, were allowed to "cross over" to receive enfuvirtide. In addition, at week 48, all of those on the control arm were offered the chance to add enfuvirtide to their regimen. Thus, while the purpose of the data collected from week 48 to 96 is to assess the durability of enfuvirtide over time, there is no longer a control group available for comparison.

The study results demonstrate the continued success of enfuvirtide-containing regimens compared to what is achieved with just a background regimen. At week 48, nearly 3 times as many participants had a viral load below 400 copies/mL on enfuvirtide compared with the control (34% versus 13%, respectively).

At week 96, 26% of the patients in the study still had viral suppression to <400 copies/mL, double what was achieved without enfuvirtide at week 48. These results are mirrored by the improvements in the CD4+ cell counts; for example, 51% of the patients on the enfuvirtide arm, versus only 16% on the control arm, had an increase of at least 50 cells/mm3 in the first year, and 39% still had that same CD4+ response on the enfuvirtide arm at week 96.

In terms of adverse events, by week 96 approximately 9% discontinued enfuvirtide due to injection site reactions. This figure, which is only slightly higher than what was seen at week 48, suggests that it is possible for many who start this agent to be maintained on it. In terms of severity, about 20% reported either moderate or severe injection site reactions, while the other 80% reported either no reactions, or only mild reactions over the 2-year period. In an analysis of other adverse events in the second year, no evidence of new drug-related adverse events was reported. For example, the rate of pneumonia on the enfuvirtide arm was stable over the 2-year time period.

These results continue to help inform the use of enfuvirtide for those in need of this drug. Because the drug is taken by self-injection, there has been greater reluctance reported to initiate this drug compared to other HIV medications, which are taken orally. Nevertheless, the data show that the majority of patients who do take enfuvirtide benefit from its use, and these benefits may persist for at least 2 years. Additional analyses are ongoing to further define the optimal timing for starting enfuvirtide, with particular focus on the diminished success observed if enfuvirtide use is delayed to the "next" switch in antivirals; these analyses are expected to be presented at this and other upcoming meetings.