August 2007
Heterosexual men and women, gay men and males who have sex with males practice anal intercourse (AI) for pleasure. Heterosexuals may also practice AI to avoid risk of pregnancy or to "maintain virginity". The few international studies available show that AI occurs all over the world -- with heterosexual couples engaging in AI in many cultures.1,2 In U.S. surveys, 35% of heterosexual women reported having had AI at some time in their lives and 6.7% of heterosexual couples practice AI at least once a month.3,4
During an act of unprotected anal intercourse, HIV is 10-100 times more easily transmitted to a receptive partner (male or female) than during vaginal intercourse. Condoms provide an effective barrier against HIV infection and some other sexually transmitted infections, such as gonorrhoea and syphilis, which may facilitate HIV transmission. However, millions of receptive sex partners find it very difficult or impossible to ensure condom use every time.
Currently in development, a microbicide is a cream or gel that could be used to reduce a person's risk of HIV infection vaginally and rectally. Rectal microbicides could offer both primary protection in the absence of condoms and back-up protection if a condom breaks or slips off during AI. For those unable or unwilling to use condoms, rectal microbicides could be a safe and effective means of reducing risk, especially if they were unobtrusive and/or enhanced sexual pleasure enough to be used consistently. Such alternatives are essential if we are to address the full spectrum of prevalent sexual practices and the basic human need for accessible, user-controlled HIV and STI prevention tools.
More than a dozen potential vaginal microbicides are currently in human trials, but it is not clear whether any of them will be suitable for rectal use. The rectum and the vagina have very different structures and natural ecologies. The vagina, for example, is a closed pouch while the rectum is part of an open-ended cavity. A greater quantity of the microbicidal product is likely to be required for adequate rectal coverage than for effective vaginal use. More immune cells with CD4 receptors and more CD4 receptors per cell also make rectal mucosa particularly vulnerable to HIV infection. The rectal lining is one cell layer thick and rather fragile compared to most of the vaginal lining, which is 40 cell layers thick. These factors further enhance rectal vulnerability to irritation, tearing and infection during sex.
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Although most microbicide research focuses on vaginal use, research and development (R&D) of rectal microbicides is a growing segment in the field. Rectal microbicide R&D includes several types of research that are underway to find answers to some of these questions. For additional research updates, visit www.irmwg.org.
It is essential that all vaginal microbicides candidates in late stage clinical testing be tested for rectal safety, because it is likely that some people will try to use them rectally in the hope of gaining some protection. A product may be very safe for vaginal use while unsafe for rectal use -- in which case people who use it rectally may actually increase their risk of infection. Rectal safety testing of vaginal products is essential so that any such products that are NOT safe for rectal use can be labelled in a way that specifically indicates what the consequences of using them rectally may be.
We now know that Nonoxynol-9 IS NOT an effective microbicide! Manufacturers started adding N-9 (a spermicide commonly used in over-the-counter birth control products) to condoms and sexual lubricants when it was shown to kill HIV in a test tube. Now we know conclusively that N-9 can irritate both rectal and vaginal tissues, possibly making it easier for HIV to reach and infect susceptible cells. In one study, lubricants containing N-9 were shown to strip surface cells off of the rectal lining, potentially enhancing its vulnerability to infection. The World Health Organization and numerous other health authorities strongly advise against the rectal use of products containing N-9, including condoms coated with N-9 (often labelled "spermicidally lubricated"). For more information, see the Global Campaign Factsheet #9 on Nonoxynol 9.
Men and women demand safe and effective rectal microbicides. The time to develop them is now! There are significant biological, sociocultural, and political barriers to the research and development of safe and effective rectal microbicides. But we must not delay efforts to develop these urgently needed products. The escalating numbers of new HIV and STI infections resulting from unprotected AI testify to the fact that having one prevention tool, condoms, just isn't enough. It is time for receptive partners of both genders to have prevention methods they can control. It is time for rectal microbicides.
Convened by AIDS Foundation of Chicago, the Canadian AIDS Society, and CHAMP, the International Rectal Microbicide Working Group is a coalition of over 500 advocates, policymakers and scientists from 35 countries on 5 continents working to advance a robust rectal microbicide research and development agenda. To get involved, join the listserv, or to learn more, visit www.irmwg.org or contact Jim Pickett at jpickett@aidschicago.org.