Just 2 months after the use of oral tenofovir
was discontinued in the VOICE trial (
JW
AIDS Clin Care Oct 3 2011), study investigators have announced that the
use of vaginal tenofovir gel is also being discontinued. The decision is
based on an interim review at 2 years, showing similar rates of HIV
acquisition in women assigned to a daily tenofovir-based vaginal
microbicide and those assigned to placebo gel (6.0% and 6.1%,
respectively). Notably, the review did not identify any safety
concerns.
The VOICE trial originally included five study arms — oral
tenofovir (Viread), oral tenofovir/FTC (Truvada), oral placebo, vaginal
tenofovir gel, and vaginal placebo gel — with each intervention
prescribed for daily use. About 1000 HIV-uninfected women were assigned to
each arm. At this point, only those receiving oral tenofovir/FTC or oral
placebo will continue as planned. The trial is expected to be completed by
mid-2012, with final results available by early 2013.
Comment: In the past 18 months, HIV prevention research has
yielded both tremendously exciting results and extremely disappointing
ones, and this news from the VOICE trial is clearly in the latter category.
Not only was the trial intended to clarify the comparative effectiveness of
oral versus vaginal-gel strategies for HIV prevention in women, but it was
also intended to be the second study required by regulatory bodies for
approval of tenofovir gel — assuming the results of the
CAPRISA
004 study could be replicated or improved upon. The negative results of
the VOICE trial confirm the complexity of using medication-based HIV
prevention strategies. Of note, the CAPRISA 004 study used a
coitus-dependent dosing regimen (12 hours prior and 12 hours after
intercourse), whereas VOICE used daily dosing. If an analogy can be made to
the
iPrEx
trial (and it remains to be seen if such analogy is appropriate), it's that
participants in HIV prevention studies seem to adhere poorly to daily
dosing and thus potentially leave some episodes of intercourse "uncovered"
by protective antiretrovirals. Details on adherence levels, drug levels in
vaginal tissues, and risk behaviors are critical for understanding the
vastly different results of VOICE and CAPRISA 004 — and also the
conflicting results of various tenofovir/FTC trials in women (
Partners
PrEP,
TDF2,
and
FEM-PrEP).
Until the detailed results of all these trials are fully presented, it is
virtually impossible to proceed with much-needed implementation research
and demonstration projects in female populations.
— Raphael J. Landovitz, MD, MSc
Dr. Landovitz is Assistant Professor, Division of Infectious Diseases,
Center for Clinical AIDS Research and Education, University of California,
Los Angeles. He reports no conflicts of interest.
Published in Journal Watch HIV/AIDS Clinical
Care December 5, 2011
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