Effectiveness

The effectiveness of enfuvirtide was demonstrated in the pivotal TORO 1 and 2 studies of nearly 2000 persons. In both studies, intent-to-treat analysis showed significantly greater reductions in viral load among those taking T-20.^{1 2}

An analysis showed that 67% of people who had a viral load below 100,000 copies/ml, a CD4 cell count above 100 cells/mm³, had previously used ten or fewer drugs, and had two or more active drugs in their background regimen were able to achieve viral suppression below 400 copies/ml at 48 weeks. ³

Adding T-20 to an effective background regimen produces the strongest and most enduring virological response. A recent analysis has shown that even adding T-20 to a background regimen consisting of drugs to which the patient is resistant reduced viral loads in the first four weeks of the study.

More than 1000 patients with advanced disease and resistance to the three older drug classes were randomly assigned to receive an optimised background regimen with or without T-20 in the TORO-1 and 2 studies. After 24 weeks, viral load decreased by an average of 1.4 to 1.7 logs in the T-20 group compared with 0.6 to 0.8 logs in the optimised background only arm. About 60% in the T-20 arm and 30% in the control arm attained a viral load below 400 copies/ml. CD4 cell gains were about twice as large in the T-20 arms.^1,4

By 48 weeks, one-quarter of people in the T-20 group and more than three-quarters in the control group had dropped out of the two studies. While only 30% in the T-20 arm achieved viral suppression below 400 copies/ml and 18% below 50 copies/ml, this was still more than twice as high as the response rates in the control arm.⁵

After one year, people who took T-20 in addition to an optimised regimen were more likely to have a significant reduction in viral load and undetectable viral load, as well as a greater increase in CD4 cell counts and longer mean survival. By 96 weeks, 55% were still taking T-20. About a quarter of those initially assigned to the T-20 group had a viral load below 400 copies/ml, though this rose to about 50% when considering only those who stayed on treatment.⁶ Recent data have also shown that T-20 is still effective in around a quarter of patients at two years’ follow-up.⁷