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Microbicides

Winter 1999/2000

A note from TheBody.com: Since this article was written, the HIV pandemic has changed, as has our understanding of HIV/AIDS and its treatment. As a result, parts of this article may be outdated. Please keep this in mind, and be sure to visit other parts of our site for more recent information!

All over the world, consistent condom use is difficult to achieve, especially within long-term relationships. Because of cultural issues, embarrassment, low self-esteem, financial dependency and/or domestic violence, millions of women simply can't or don't insist on male condom use. In studies done on the subject, consistent condom use is rarely reported by more than 50% of those surveyed. Most surveys of heterosexual primary partnerships show that condom use happens 20% of the time or less. The only studied populations that have reported using condoms regularly for more than half of their acts of intercourse are serodiscordant couples and commercial sex workers. For sex workers, who may get paid more if they don't insist on condom use, economic need may often overwhelm their need for self-protection. Even individuals who regularly use condoms with "outside" partners have proven unwilling or unable to use them with their primary partners. And, in cultures in which childbearing is directly linked to a person's self worth, the prospect of childlessness often outweighs the risk of HIV infection in women's minds.

All in all, a woman's ability to refuse to have sex without a condom usually depends more on other factors in her life than on her perceptions of HIV risk.

According to the Joint UN Programme on AIDS ("UNAIDS"), unprotected sex with an HIV-positive man is by far the leading cause of HIV infection among women, and the result is that more women than men are now getting infected with HIV annually. Since a woman's ability to use condoms ultimately depends on the cooperation of her male partner, this number is likely to increase. Even the internal or "female" condom is visible when in place and, thus, is not a method most women can use without their partner knowing. What is needed is an easily accessible, inexpensive, safe, effective prevention method -- "non-condom alternatives" that would give the millions who can't or don't insist on condoms a way of protecting themselves from HIV and other sexually transmitted diseases (STDs).

Every day, 6,300 additional women worldwide contract HIV and hundreds of thousands more are infected with other sexually-transmitted diseases. In developing countries, STD's excluding HIV are the second leading cause of illness, disability and death among women of reproductive age. In the United States, there are 15 million new cases of "non-HIV" STDs each year, the majority in women, most under age 24 and many in their teens. According to government estimates, by 2010 at least half of all Americans infected with HIV will be women. In fact, in some parts of the country, we're there already. In Florida, for example, young women constituted 50% of the new AIDS cases reported among people between 13-24 during the years 1995-1997.

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Enter "microbicides" -- the alternative of the future. Applied in the vagina or rectum, these compounds, in different formulations, will act in various ways to reduce the transmission of STDs, including HIV. While such products are also needed for women and men who have anal sex, virtually all the microbicide research now under way focuses on vaginal use.

So what will these products be like? Similar to birth control products that have been sold over the counter for decades, microbicides could be produced in many forms: suppositories, films, gels or creams inserted with a disposable or reusable applicator, and even sponges or rings inserted into the vagina that release a microbicidal compound slowly over time. Some will be formulated as contraceptive or, for those wanting pregnancy without fear of infection, as non-contraceptive.

Many people want to know, "How does a microbicide work?" This question has several answers.The product leads being pursued work in different ways. Some microbicides work by boosting the body's natural defense systems, others introduce new substances to destroy pathogens or chemically block their entry into human cells, and still others create a type of physical barrier. The most promising products will probably combine several of these approaches. Here are a few examples of microbicides under development:

Antibiotic peptides are small protein molecules that form part of the body's first line of defense against infection. These peptides line every surface of the body -- eyes, skin, lungs, tongue and intestinal tract -- and kill bacteria within minutes of contact. If applied in concentrated quantities at the site of potential infection, these peptides may kill off pathogens before they infect the body.

Buffer Gel works by maintaining the natural acidity of the vagina in the presence of semen. The healthy vagina is normally about pH 4.2, an environment too acidic for HIV to survive. Semen, however, is alkaline (basic) and during intercourse the pH of the vagina becomes basic, allowing HIV to survive. Buffer Gel keeps the vagina acidic even during intercourse and creates a physical barrier that inhibits the passage of pathogens into the vaginal and cervical epithelium.

Carrageenan is an inexpensive substance derived from seaweed and widely used as a food additive (for example, to thicken ice cream). Carrageenan forms a tasteless gel that coats the vagina, possibly preventing HIV from entering the vaginal epithelium. Alternatively, carrageenan gel can be formulated with Nonoxynol-9 to make a combination product.

Detergents and surfactants work by disrupting the outer membranes of cells and the envelopes (outer shell) of viruses. This is the mechanism of action of Nonoxynol-9, the active ingredient in most spermicides sold in the United States.

"Invisible condom" is how researchers describe non-toxic polymer-based gels that serves as a barrier against viruses and bacteria.

Lactobacillus crispatus (LB) suppository works by re-colonizing the vagina with hydrogen-peroxide producing Lactobacillus. Lactobacillus crispatus is one of many bacteria that live normally in the healthy vagina (a sister species of lactobaccilli is found in yogurt). LB helps keep the vagina free from infection by producing hydrogen-peroxide, a substance that is highly acidic. When the ecology of the vagina is somehow disrupted -- through infection, douching, or poor hygiene -- the LB bacteria can die off, leading to a condition known as bacterial vaginosis (BV).

"Plantibodies" represent an innovative approach to microbicide development using genetically engineered plants to produce human antibodies active against a range of sexually transmitted infections (STIs). Antibodies are one of the body's main defense systems, and the basis for vaccine technology. Today, scientists have found ways to isolate the particular antibodies that counteract HIV and other STIs, and to mass produce them relatively inexpensively using genetically engineered plants. This technology raises the possibility of delivering anti-HIV antibodies directly to the vagina, allowing them to combat pathogens before actual infection occurs.

PMPA Gel works in the same way as some of the anti-retroviral drugs currently used for therapy: it interrupts the replication of the virus once it enters cells. The hope is that PMPA (Tenofovir) could be absorbed by cells in the vaginal epithelium and then stop the virus in its tracks once it enters the outer cells of the vaginal wall. Many anti-retroviral drugs that were initially explored as potential AIDS therapies were later abandoned because they could not be absorbed easily into the bloodstream; these same compounds might be perfect candidates for a microbicide because they could be topically applied and not absorbed systemically.

Pro-2OOO Gel contains a synthetic polymer that binds to the HIV virus, thereby disrupting binding of the virus to target cells. The gel probably works in a similar fashion to block chlamydia and HSV-2 infections.

The basic idea is that microbicides will also be, like condoms, convenient, simple to use, inexpensive, available without a prescription, and appropriate for distribution in stores, clinics, kiosks and by peer health educators.

It is important to note that microbicides are not expected to be fully as effective against some infections as internal ("female") and external ("male") condoms. Obviously, it is always safer to keep a virus or bacteria from getting into one's body in the first place than it is to try to disable it once it's there. But for those for whom consistent condom use is not an option, an effective microbicide will be much safer than unprotected sex. Couples already using condoms will also benefit from microbicides as something that can be used with a condom for added protection. In the future, some microbicides may also be developed in other formulations such as a mouth rinse for protection during oral sex, a vaginal wash that can be used by HIV-positive women prior to childbirth as a low-cost way of reducing risk of perinatal transmission, and applications for post-coital use to reduce risk of infection after forced sex or condom failure. And, as better microbicides are developed, they will be designed to be "bi-directional"; in other words, use of a vaginal microbicide will inactivate HIV present in the vaginal secretions , thus protecting her partner, as well as protecting a woman from HIV in her partner's semen.

With concerted, international demand and the kind of financial investment and government priority this critical public health technology deserves, we could have new microbicides on the market within five years. Millions of women and men in all cultures and countries must be able to protect themselves, and condoms just aren't enough. For more information on how you can get involved in advocacy, as an individual or as an organization, please contact the Center for Health and Gender Equity (CHANGE) at 301-270-1182 and ask for Megan Gottemoeller. You can also contact Megan by e-mail at mgottem@genderhealth.org or just drop in on the web site at www.genderhealth.org. For information about what's going on in microbicide research and development, contact Polly Harrison at the Alliance for Microbicide Development at 301-588-8091 or by email at pharriso@aol.com.


Qualities a Microbicide Should Have
  • applicable hours before sex
  • not messy or "leaky"
  • able to spread rapidly and
  • evenly over the vagina and cervix
  • long-acting
  • look, smell and taste OK
  • able to prevent infection without disrupting or irritating the delicate tissues
  • bioadhesive (able to form protective barrier against STD pathogens)
  • protective against a range of STDs
  • acid-buffering (maintains normal acidity [pH] of vagina in presence of semen)
  • protective of natural vaginal environment ("friendly flora"), perhaps even boosting natural vaginal defense mechanisms




Anne Forbes is the Field Organizer for the Global Campaign for Microbicides and Women-Controlled STI/HIV Prevention Alternatives and Polly Harrison, PhD, is the Director of the Alliance for Microbicide Development in Maryland.


A note from TheBody.com: Since this article was written, the HIV pandemic has changed, as has our understanding of HIV/AIDS and its treatment. As a result, parts of this article may be outdated. Please keep this in mind, and be sure to visit other parts of our site for more recent information!



  
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This article was provided by AIDS Community Research Initiative of America. It is a part of the publication CRIA Update. Visit ACRIA's website to find out more about their activities, publications and services.
 
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