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CATIE News - Study drops oral tenofovir as HIV prevention in a women's study

2011 Oct 12 - The burden of HIV infection is largely borne by people in sub-Saharan Africa, particularly girls and women. Behavioural messages that encourage abstinence, monogamy and use of condoms have had, according to researchers, only a limited long-term impact on the spread of HIV in that region. This situation arises in part because women do not have control over their sexuality and face many obstacles to achieve social, economic and political equality. Needless to say, more options for preventing HIV transmission are needed. 

PrEP

Pre-exposure prophylaxis (PrEP) is a term given to any anti-HIV therapy that can be taken prior to exposure to HIV in the hope that it will protect the user from HIV infection. PrEP can take the form of pills taken orally or creams or gels applied to the vagina, anus or penis. Creams or gels with anti-HIV activity that are applied to the genitals are called microbicides. Creams or gels that contain anti-HIV drugs are considered a topical form of PrEP.

Topical and oral forms of PrEP continue to be studied so that researchers can be certain about their effectiveness. Many formulations of PrEP use the antiviral drug tenofovir (called Viread when used in pill form) or combinations of tenofovir and another drug called FTC (sold as a fixed-dose co-formulation pill called Truvada).

Clinical trials have found that PrEP can reduce a person's relative risk of becoming infected with HIV. However, the preventive effect of anti-HIV drugs taken in this way is less than 100% and is strongly dependent on a person's ability to take the drug as directed, a behaviour called adherence. Indeed, in a trial called Caprisa, in which researchers tested a tenofovir-containing vaginal gel used before and after sex against a placebo gel in heterosexual women, they found that the gel reduced the risk of becoming infected with HIV by 39%.

Another trial (called iPrEx) in gay and bisexual men found that when compared to placebo a Truvada pill taken daily reduced the relative risk of HIV infection by 44%.

Two other studies (TDF2 and Partners PrEP) found that a daily Truvada or tenofovir pill was able to reduce the risk of acquiring HIV in heterosexual people. Surprisingly, a study called FEM-PrEP was stopped early because it seemed that daily Truvada was not able to reduce the risk of HIV infection among heterosexual women. The reason(s) for the disappointing results in FEM-PrEP are not yet known.

VOICE

In Southern Africa, researchers are conducting a study called VOICE (Vaginal and Oral Interventions to Control the Epidemic), sponsored by the Microbicide Trials Network and the U.S. National Institutes of Health (NIH). It has recruited more than 5,000 women. Researchers randomly assigned women to each of the following five study arms:

  • daily tenofovir vaginal gel
  • daily placebo vaginal gel
  • daily tenofovir tablet
  • daily Truvada tablet
  • daily placebo tablet

This type of study design will enable researchers to compare the effectiveness of different regimens in preventing HIV infection when VOICE is completed.

Monitoring

Many trials have an independent oversight committee called a Data and Safety Monitoring Board (DSMB). The role of a DSMB is to periodically review the data collected from the study and to stop or modify the study if there are concerns about the safety of participants or the effectiveness of interventions being studied.

The Microbicide Trials Network recently stated that after reviewing the available data the DSMB concluded that "it is not possible to show whether oral tenofovir tablets were any better than placebo" in their ability to prevent HIV infection (similar to the FEM-PrEP study that was stopped early). The DSMB recommended that women in VOICE who were receiving tenofovir tablets stop taking them, but it had no concerns about the safety of tenofovir. The DSMB noted that women in the other four arms of the study should continue taking their assigned intervention(s).

These results are surprising because the Partners PrEP study found that a daily tenofovir pill did reduce the risk of HIV infection when used by heterosexual women.

All participants in VOICE will be told about the DSMB's recommendations. Although the use of a daily tenofovir pill for PrEP has been stopped, women in the study are continuing to take the daily Truvada pill and the daily tenofovir gel.

Researchers are not certain why oral tenofovir did not significantly protect women in VOICE but this may become apparent when the full results of the study are released next year. As the trial is continuing, a complete analysis of the data is not expected to become available until the end of 2012.

Resources:

CATIE Prevention in Focus article on PrEP
CATIE Fact Sheet on PrEP
CATIE-News story on iPrEx trial
CATIE-News story on FEM-PrEP trial
CATIE-News story on TDF2 and Partners PrEP
 

                                                                                                              -Sean R. Hosein

REFERENCES:

•  Abdool Karim Q, Abdool Karim SS, Frohlich JA, et al. Effectiveness and safety of tenofovir gel, an antiretroviral microbicide, for the prevention of HIV infection in women. Science . 2010 Sep 3;329(5996):1168-74. 

•  Baleta A. Antiretroviral vaginal gel shows promise against HIV. Lancet . 2010 Jul 31;376(9738):320.

•  Baeten J. Antiretroviral pre-exposure prophylaxis for HIV-1 prevention among heterosexual African men and women: the Partners PrEP Study. In: Program and abstracts of the 6 th International AIDS Society Conference on HIV Pathogenesis, Treatment and Prevention , 17-20 July 2011, Rome. Abstract MOAX0106, 2011.

•  Thigpen M, Kebaabetswe PM, Smith DK, et al. Daily oral antiretroviral use for the prevention of HIV infection in heterosexually active young adults in Botswana: results from the TDF2 Study. In: Program and abstracts of the 6 th International AIDS Society Conference on HIV Pathogenesis, Treatment and Prevention , 17-20 July 2011, Rome. Abstract WELBC01.

•  Microbicide Trials Network. MTN statement on decision to discontinue use of oral tenofovir tablets in VOICE, a major HIV prevention study in women. Press release . 28 September 2011.

From Canadian AIDS Treatment Information Exchange (CATIE). For more information visit CATIE's Information Network at http://www.catie.ca

Source: CATIE: CANADIAN AIDS TREATMENT INFORMATION EXCHANGE


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