There has been a lot of concern regarding the contribution of many antivirals to changes in body shape -- specifically the changes in body fat called lipodystrophy. While enfuvirtide (T-20, Fuzeon) is an antiviral, it works by a completely different mechanism, specifically blocking the attachment of HIV to human cells. Given this difference, it is important to assess whether enfuvirtide has any impact on body composition or other metabolic toxicities such as lipid disturbances.

These results come from an analysis of the "TORO" studies, which compared a standard regimen of antivirals versus the addition of enfuvirtide to a standard combination for patients with multidrug-resistant HIV. Measures of fat distribution were done by DEXA scanning and CT scans in a subset of about 150 people in these studies. In addition, all participants had body shape and blood chemistry measurements done.

The results were quite clear. Over the 48 weeks of the study, there was no negative impact -- and perhaps a trend actually favoring the arm containing enfuvirtide for less fat redistribution and other adverse effects. Specifically, the rate was 11.7% for all adverse events of this type (lipodystrophy, diabetes, heart disease and lipid abnormalities) for the control arm, and 9.2% for the enfuvirtide arm. There were no differences seen in patients' waist/hip measurements in either arm over time. There was a suggestion from the DEXA scans for recovery of subcutaneous fat on the enfuvirtide arm, and this was also seen on the CT scan. An increase in visceral fat was seen more in the enfuvirtide arm than the control arm, although the authors noted that this might, in part, reflect the changes associated with recovery from HIV wasting. Finally, neither lipid differences nor changes in blood glucose were seen.

Overall, the authors conclude that there were no adverse events related to these troubling metabolic changes associated with the use of enfuvirtide. Specifically, there were trends favoring improvements in terms of fewer reports of lipodystrophy, and evidence of recovery of limb fat on the enfuvirtide arm. These results support that the unique mechanism of action of enfuvirtide is also distinct with regard to the side effects we see with the other classes of antivirals. While improvements continue to be explored in these other classes as well, it appears from studies of enfuvirtide that the drug doesn't add any significant additional risk for the metabolic disturbances that complicate the treatment of HIV.

Reference

Abstract: The Effects of Enfuvirtide Therapy on Body Composition and Serum Lipids Through 48 Weeks in the TORO Trials (Poster 715)
Authored by: D. A. Cooper, P. Reiss, K. Henry, M. Nelson, M. O'Hearn, P. Piliero, J. Reynes, K. Arasteh, J. Chung, D. Guimaraes, T. Kinchelow, A. Bertasso, The TORO 1 and TORO 2 Study Groups
Affiliations: Natl. Ctr. in HIV Epidemiology and Clin. Res., Univ. of New South Wales, Sydney, Australia; Academic Med. Ctr., Amsterdam, The Netherlands; Hennepin County Med. Ctr., Minneapolis, MN; Chelsea and Westminster Hosp., London, UK; Oregon Hlth. and Sci. Univ., Portland, OR; Albany Med. Coll., NY; Hosp. Gui de Chauliac, Montpellier, France; EPIMED c/o Vivantes Auguste-Viktoria-Klinikum, Berlin, Germany; Roche, Nutley, NJ