Microbicides

What is a Microbicide?

 

A microbicide is a product designed to prevent or greatly reduce the risk of acquiring HIV and other sexually transmitted diseases (STDs) during sexual activity.  In recent years there has been a great surge of research and laboratory trials taking place in hopes that a successful micorbicide will soon be developed.  The majority of research being conducted has focused on vaginal microbicides, however as demand for rectal microbicides increases, so has the attention and efforts of researchers.

 

Virtually all of these products are 'topical' microbicides. A topical microbicide can take many forms, such as a foam, cream, or gel, which is applied directly to the vagina or rectum. It could also be a suppository (medication that is inserted into a body cavity like the vagina or rectum).

 

A New Tool in the Prevention Tool Box

 

If a truly successful microbicide is discovered and marketed it would be a welcome addition to current HIV prevention tools! It would not, however, replace other prevention tools like male condoms, female condoms, dental dams, or latex gloves. The proper and consistent use of a condom during intercourse is still your best bet for preventing HIV transmission, and that is unlikely to change even if a marketable microbicide is found.

For those who consistently use condoms, a microbicide could be used as an added preventive measure. For those who, for whatever reason, do not always use condoms, a microbicide could be used alone to reduce risk of HIV transmission.

Women and Vaginal Microbicides

Male-to-female transmission of HIV and female-to-male transmission of HIV are not the same. Women are twice as likely as men to contract HIV from a single act of unprotected sex because of their biological differences.[1] This is one reason women are disproportionately impacted by HIV/AIDS.

In the United States women comprise a growing share of new AIDS cases each year. The proportion of AIDS cases among women has more than tripled since 1986 from 7% to 23% ³. In sub-Saharan Africa, women make up 57% of those living with HIV, and 75% of young people infected are women and girls.[2]

New HIV prevention strategies for women are clearly needed. A microbicide is one such strategy. For millions of women around the world, negotiating condom use with a partner can be extremely difficult, if not impossible. A microbicide would help to address this by empowering women to take action and reduce their risk of HIV infection on their own. Microbicides would not just benefit women, though. In theory, such a microbicide could also prevent HIV transmission from a woman to her male partner.

A great deal of vaginal microbicide research has been conducted over the years, but it was not until 2010 that successful results were returned.

CAPRISA 004 was a microbicide trial of a 1% tenofovir gel tested among 889 South African women.  The results which were released on July 20, 2010 at the International AIDS Conference in Vienna, showed an overall 39% fewer infections among women who received the 1% tenofovir gel compared to those who received the placebo gel; and after just a year of use of the 1% tenofovir gel, women had 50% fewer HIV infections than those in the placebo group. Additionally, those women who adhered to the prescribed application regime of two doses of tenofovir gel for more than 80% of sexual acts, showed a 54% lower risk of contracting HIV.

 

The CAPRISA 004 trial also returned promising results in protection against the acquisition of the herpes simplex virus (HSV-2).  The tenofovir gel showed a 51% protective effect against the acquisition of the herpes simplex virus.  This was an exciting addition because those who are HSV-2 positive are more likely to acquire and transmit HIV than those who are negative.[3]

Rectal Microbicides

Less research has been done on rectal microbicides, than vaginal microbicides. Unfortunately, just because a microbicide works vaginally, does not mean it will also work rectally. There are many differences between the rectum and vagina which include:

• The vagina is an enclosed space, while the anus, rectum, and colon are continuous and open-ended.
• The vaginal epithelium (membrane tissue) is 40 cell layers thick, while the epithelium of the rectum is only 1 cell layer thick, and therefore more fragile.
• The human vagina is a moderately acidic environment, the rectum is not; Both have different ecologies.[4]

The current focus is on testing the effectiveness of vaginal microbicides in the rectum; however money seems to be the limiting factor as funders have yet to show enough will to commit to a full-scale efficacy trial specifically for rectal microbicides. Researchers have completed a phase 1 clinical trial to test the rectal safety of UC-781 an antiretroviral being developed for vaginal use.[5]  While the results have not been published yet, a co-investigator of the research, Ian McGowan said that UC-781 seemed to be safe and acceptable.

Rectal microbicides are currently in development in the form of a lubricant gel, douche or enema that can be used rectally to reduce a person's risk of HIV infection in the absence of condoms or in addition to condom use.  A successful rectal microbicide is needed because a single act of unprotected anal intercourse is 10-20 times more likely to result in HIV infection compared to unprotected vaginal intercourse.  As of 2010 laboratory tests and animal studies of rectal microbicides (RM) are being conducted to prepare products for safety trials.

Amongst those working to see that rectal microbicide research is further developed is the International Rectal Microbicide Advocates (IRMA), which is comprised of over 1,000 advocates, policymakers, and lending scientists from 6 continents. Their mission states that they are:

Working together to advance a robust rectal microbicide research and development agenda- with the goal of creating safe, effective, acceptable and accessible rectal microbicieds for the women, men, and transgender individuals around the world who engage in anal intercourse.[6]

The State of Microbicide Research

More than 60 products have been evaluated as potential microbicide candidates. The majority of these products have undergone preclinical evaluation, some have advanced into human studies. To be successful in reducing HIV transmission the ideal topical microbicide must have several characteristics: 

• it must be safe and effective
• inexpensive and widely accepted
• available in both spermicidal and non-spermicidal formulations
• able to be used without partner knowledge. 

Even a partially effective microbicide might have a profound impact on the dynamics of HIV transmission. In fact, researchers have developed a mathematical model that shows that if even a small proportion of women in lower income countries using a 60% efficacious microbicide in half the sexual encounters where condoms are not used, could avert 2.5 million HIV infections over 3 years (hptn.org).

For more information on Microbicide Research

Alliance for Microbicide Development
8484 Georgia Ave, Suite 940, Silver Spring, MD 20910
              (301) 587-9690         (301) 587-9690
www.microbicide.org
The Alliance for Microbicide Development is a global, non-profit organization whose sole mission is to speed the development of safe, effective, and affordable microbicides to prevent sexually transmitted infections, most critically HIV/AIDS.

Global Campaign for Microbicides (c/o PATH)
1800 K Street NW, Suite 800, Washington, DC 20006
              (202) 822-0033         (202) 822-0033
www.global-campaign.org
The Global Campaign for Microbicides is a broad-based, international effort to build support among policymakers, opinion leaders, and the general public for increased investment into microbicides and other user-controlled prevention methods.

International Rectal Microbicides Advocates (IRMA)

www.rectalmicrobicides.org

IRMA is comprised of over 1,000 advocates, policymakers and leading scientists from 6 continents working together to advance a robust rectal microbicide research and development agenda - with the goal of creating safe, effective, acceptable and accessible rectal microbicides for the women, men, and transgender individuals around the world who engage in anal intercourse.