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Viread And Truvada May Be Effective At Preventing HIV Infection In Heterosexuals

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Published: Jul 13, 2011 12:54 pm
Viread And Truvada May Be Effective At Preventing HIV Infection In Heterosexuals

Results released today from two new African clinical trials show that the anti-HIV drugs Viread and Truvada are effective at preventing transmission of HIV in heterosexual couples when combined with regular condom use and other traditional prevention measures.

When taken daily, the antiretrovirals reduced transmission risk by 60 percent to 70 percent. Due to the strength of the results one of the two trials was modified to discontinue the placebo group early, with all participants being placed on the drugs for prevention purposes.

“These are exciting results for global HIV prevention. We now have findings from two studies showing that [pre-exposure prophylaxis] can work for heterosexuals, the population hardest hit by HIV worldwide,” said Dr. Kevin Fenton, director of the Centers for Disease Control’s National Center for HIV/AIDS, Viral Hepatitis, Sexually Transmitted Diseases, and Tuberculosis Prevention, in a press release.

The studies are particularly relevant for serodiscordant couples, in which one partner is HIV positive and the other is HIV negative.

Based on the results, the United States Centers for Disease Control and Prevention (CDC) has stated that it will begin working on guidelines for heterosexual men and women in the U.S.

“The next important step is to fully review the data and assess when and how [pre-exposure prophylaxis] should best be used for HIV prevention among heterosexuals,” said Dr. Jonathan Mermin, director of the CDC’s Division of HIV/AIDS Prevention.

Viread And Truvada Decrease HIV Infection Risk

Viread (tenofovir), which is also a component of Truvada (emtricitabine/tenofovir), is an antiretroviral drug marketed by Gilead Sciences. Results from a previous clinical trial showed that a daily dose of Truvada reduced the risk of HIV infection in men who have sex with men by 44 percent (see related AIDS Beacon news).

The purpose of the two new clinical trials was to see if Viread and Truvada are similarly effective in heterosexual serodiscordant couples. The strategy of taking antiretrovirals to prevent HIV infection is known as pre-exposure prophylaxis.

The first trial, conducted by the CDC in Botswana, included 1,219 men and women aged 18 to 39 years. Half the participants received Truvada once daily while the other half took a placebo. All participants were instructed in HIV prevention, including condom use, and tested regularly for HIV.

Preliminary results showed that 9 of 601 participants taking Truvada (1.5 percent) contracted HIV during the study period, compared to 24 of 599 participants taking a placebo (4 percent), for a total reduction in HIV infection risk of 63 percent.

Further analysis showed that participants with steady access to the drugs (excluding those who may not have had access during the entire study period) had an overall risk reduction of 78 percent. The CDC reported no significant safety concerns, with the most common side effects being nausea, vomiting, and dizziness.

The trial is completed but the CDC is still in the process of analyzing the results, including the impact of adherence on the drug’s efficacy.

The second clinical trial, conducted by the University of Washington in Kenya and Uganda, included 4,758 serodiscordant couples. One third of the HIV-negative partners in the study received Viread once daily, one third took Truvada once daily, and the remaining one third received a placebo. As in the CDC trial, all participants were instructed in safe sex practices and tested regularly for HIV.

Results showed a total of 18 new HIV infections among the partners taking Viread, 13 in partners taking Truvada, and 47 among those taking a placebo. The reduction in infection risk was found to be 62 percent for patients taking Viread and 73 percent for patients taking Truvada, although the difference between the drugs was not considered large enough to be statistically significant.

The researchers also found high levels of treatment adherence, with more than 97 percent of assigned doses actually taken. The rates of serious medical problems during the trial were similar for patients receiving the antiretrovirals and those receiving the placebo.

The trial is ongoing but participants receiving the placebo have been switched to taking either Viread or Truvada.

A third clinical trial testing the efficacy of once-daily Truvada in pill form versus as a vaginal gel for pre-exposure prophylaxis is still ongoing.

CDC: Guidelines On Pre-Exposure Prophylaxis For Heterosexual Men And Women Are Coming

As a result of the two successful trials, the CDC plans to release guidelines in the U.S. for use of Viread or Truvada in heterosexual couples. The CDC has recommended that couples wait for the guidelines, which will include topics like how to handle pregnancies, before using the drugs as a preventative measure.

However, for those considering taking Viread or Truvada now, officials at the CDC have issued the following recommendations:

  • HIV-negative individuals should confirm, via HIV testing, that they are still HIV negative before starting pre-exposure prophylaxis. They should also continue to be tested regularly for HIV.
  • Antiretrovirals taken as a preventative measure should always be combined with other safe sex strategies, such as regular condom use. They are not meant to be a stand-alone barrier to infection.
  • The drugs must be taken daily.
  • Antiretrovirals should only be used after consulting with a physician and in conjunction with regular monitoring.

The CDC also noted that there is no information yet on whether pre-exposure prophylaxis is effective in injection drug users. There is also insufficient information to provide a recommendation to women who are pregnant, planning to become pregnant, or breastfeeding.

Pre-Exposure Prophylaxis Gains Steam But Is Still Somewhat Controversial

The use of pre-exposure prophylaxis in the U.S. is still somewhat controversial. The AIDS Healthcare Foundation (AHF), a California-based treatment and advocacy group, recently asked the Food and Drug Administration (FDA) not to approve Truvada for pre-exposure prophylaxis, based on the trial results for men who have sex with men (see related AIDS Beacon news).

“The first of our numerous concerns is that the…study results do not pass the threshold for effectiveness. The 44 percent efficacy that was achieved is well below the threshold generally agreed upon as necessary to be considered effective,” wrote AHF.

“The impact of a prophylactic with an efficacy rate of 60 percent would be considered low. It is unclear why the threshold of acceptability has been lowered so significantly in the case of [Truvada].”

The AHF argued that the drug was not effective enough in preventing HIV transmission and could lead to riskier sexual behavior and transmission of drug-resistant HIV. In addition, the AHF pointed to an earlier study showing that Truvada was ineffective at preventing HIV infection in women; it is still unclear why that study was less successful.

However, the new results, which show higher efficacy rates for heterosexual men and women, could increase the probability of Truvada or Viread receiving FDA approval for pre-exposure prophylaxis. Even if not approved, the drugs could still be prescribed “off-label” – for a purpose other than a drug’s approved function – but Gilead would not be able to market the drugs for pre-exposure prophylaxis and insurance companies and government health plans may be less likely to cover it.

For more information, please see the press releases from the CDC and the University of Washington (pdf).

Photo by Lee Nachtigal on Flickr – some rights reserved.
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