Important note: Information in this article was accurate in 2002. The state of the art may have changed since the publication date.
AIDScience (01.28.02) Vol. 2; No.1 (AIDScience.org/articles/aidscience015.asp) - Friday, February 01, 2002
Janneke van de Wijgert; Christiana Coggins
A microbicide is a product applied topically inside the vagina or rectum to prevent infection with HIV and potentially a number of bacterial and viral STDs. These may take the form of a gel, cream or suppository and may or may not be spermicidal (have a contraceptive effect). There are some indications that some microbicides may be used to prevent transmission of HIV from women to their male partners and they may be versatile for use in the rectum for anal sex.
The identification of novel microbicidal compounds is a rapidly expanding area of HIV prevention research. An estimated total of 56 products are currently in the pipeline: 34 are in pre-clinical stages; 15 are in phase I safety trials, four are in Phase II expanded safety and preliminary effectiveness trials (Savvy cream, Emmelle gel, Lactobacillus crispatus suppository, and Praneem Polyherbal suppository), and three are about to enter Phase II/III trials (BufferGel and Pro-2000 gel), or Phase III trials (Carraguard gel) effectiveness trials.
The candidates fall into four categories or combination of categories: 1) Products that kill or inactivate infectious pathogens - these include detergents (like nonoxynol-9, Savvy), peroxides, lipids, plant extracts (Praneem, gossypol), antimicrobial peptides, monoclonal antibodies and acidic buffers. Early hopes were pinned on over-the-counter spermicides containing nonoxynol-9 as potential microbicides. Recent studies have shown the nonoxynol-9 products are ineffective against HIV and most STDs and increase the risk of genital ulceration. 2) Products that block fusion, i.e. prevent attachment to the mucosal surface of target cells - these include those that specifically target HIV surface proteins or HIV receptors and non-specific blockers that are active against multiple organisms (Carraguard, Emmelle, Pro- 2000 and Usercell). 3) Products that inhibit post-fusion activity by interrupting HIV life cycle after the virus has infected the cell - these included nucleoside/tide RT inhibitors; non-nucleoside/tide RT inhibitors; protease inhibitors; and post-binding fusion inhibitors. 4) Products that enhance naturally occurring vaginal defense mechanisms. The natural vaginal flora of healthy women is dominated by lactobacilli, which produce a number of compounds that inhibit pathogenic microorganisms. These compounds also maintain a low, acidic pH in the vagina. Other important defenses are naturally occurring antimicrobial peptides and antibodies in the vagina. A few newly developed microbicides aim to enhance these natural defenses. They may be of particular relevance to those countries in sub-Saharan Africa where almost half the women of childbearing age have bacterial vaginosis, characterized by a lack of vaginal lactobacilli. (Products include Lactobacillus crispatus suppository, BufferGel, Acidform gel, Protegrins, Plantibodies [monoclonal antibodies]). About 35 of the products currently in research are contraceptives as well as microbicidal.
Much progress has been made on microbicides but many challenges remain. Badly needed is a significant increase in investment from both the public and private sectors. To date, no major pharmaceutical company has made a significant investment in this research and development. Innovative public-private partnerships, similar to the International AIDS Vaccine Initiative, are being explored.
Microbicides, once proven effective, need to be available and accessible to all women who need them. Developers should aim for over-the-counter availability and international agencies and governments should begin early to explore distribution networks, pricing, local manufacturing, education, regulatory processes and increased awareness.
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