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New Tenofovir Prodrug (TAF): One Study Whose Impact Will Last Well Beyond CROI 2013

By Josep M. Llibre, M.D., and Benjamin Young, M.D., Ph.D.

March 14, 2013

Tenofovir disoproxil fumarate (TDF, Viread) is an industry standard component for HIV regimens around the world. While very potent and generally very well tolerated, TDF is associated with increased risks of long-term renal and bone toxicity. These matters will likely grow in concern with an ever longer-lived and aging population of people living with HIV.

For these reasons, the presentation of a next-generation tenofovir prodrug, tenofovir alafenamide fumarate (TAF), was of great interest. TAF appears to be preferentially concentrated into lymphoid cells, with a roughly 5-fold increase in PBMC tenofovir exposure and ~90% reduction in plasma AUC.

Results of Gilead Sciences' phase 2, randomized, placebo-controlled clinical trial comparing fixed-dose combinations of TAF/emtricitabine/cobicistat/elvitegravir (E/C/F/TAF) with TDF/emtricitabine/cobicistat/elvitegravir (STB, Stribild) showed similar effectiveness, but less renal or bone toxicity. After 24 weeks of treatment, the two groups had similar virologic responses (87.5% E/C/F/TAF vs. 89.7% of STB, weighted difference -4.9% [95%CI: -15.7, 5.9]) and similar CD4+ cell responses. The TAF-containing fixed-dose combination was associated with statistically significantly lower declines in serum creatinine and estimated glomerular filtration rate, and no differences in markers of renal tubular injury. Likewise, TAF may be better for bones than TDF. DXA analysis of bone mineral density (BMD) showed significantly less loss of BMD in TAF recipients than TDF recipients, both in spine and hip.

Which other studies presented at CROI 2013 will have lasting impact long after memories of the conference itself have faded? Read more of Dr. Llibre and Dr. Young's top picks.

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