The results of the large international trial of the first approved fusion inhibitor, enfuvirtide (ENF, T-20, Fuzeon), have been presented several times over the past year. These studies, known as the TORO studies, generally demonstrated an improved response in patients who had enfuvirtide added to a new background regimen, versus patients who switched to a new background without enfuvirtide.

Because enfuvirtide must be given by self-injection twice a day -- a hurdle for at least some patients -- this study explored whether there are early benchmarks of virologic response that could be useful in predicting likely patient response during the subsequent 1 to 2 years.

Having this information could be a helpful motivator for people who are just beginning treatment with enfuvirtide, given that a response at week 12 could be used to support adherence to a new and somewhat challenging regimen.

This analysis used a patient's viral load and CD4+ cell count response at week 12 to predict what would be observed in the following 2 years. For example, over 85% of patients who experienced at least a 50-cell increase in their CD4+ cell count by week 12 were found to maintain this response for 2 years.

Further, almost 50% of those who had more than a 50-cell increase at week 12 also had an increase of at least 150 cells by week 48.

Similarly, a patient's viral load response at week 12 was predictive of his or her future outcomes. Using a benchmark of at least a 1-log drop in viral load at week 12, 61% of patients whose viral load dropped by at least 1 log by week 12 also had a viral load of less than 400 copies/mL by week 48. In comparison, only 2% of patients had a viral load of less than 400 copies/mL at week 48 if their viral load had not declined by at least 1 log by week 12.

Of note, there were good immunologic responses even in people who did not achieve a 1-log viral load drop by week 12. For example, for those who had neither a 1-log drop in viral load nor a 50-cell increase in their CD4+ cell count by week 12, they still had about a 33% chance to experience at least a 50-cell increase in their CD4+ cell count on an enfuvirtide-based regimen at the end of a year, and this was durable to the second year.

These data are helpful for patients facing a treatment decision about starting enfuvirtide. It is fair that many patients will want to see some evidence of activity with this new regimen, and these results allow clinicians to connect the early responses observed in patients during the first 3 months to what is likely to be seen in the next few years.

These results are similar to those of studies done on people taking interferon for hepatitis C in which the benchmark of 12 weeks also predicts longer-term response. This kind of information is particularly important when asking patients to use a medication that has some hurdles to simple daily use (e.g., an injection).

The benefit of such predictive information is that it can help patients reach a decision when debating whether to start taking enfuvirtide. Through these data we have early evidence allowing us to provide that needed support to patients while they are still adjusting to a new regimen.