What they are
Microbicides are compounds that can be applied inside the vagina or rectum to protect against sexually transmitted infections (STIs) including HIV. They can be formulated as gels, creams, films, or suppositories. Microbicides may or may not have spermicidal activity (contraceptive effect). At present, an effective microbicide is not available.
Why they are Important
It is important to support the development of microbicides because:
How they Work
There are different ways in which microbicides act to prevent infection with genital pathogens. Some microbicides (e.g Carraguard®, Cyanoviran®, cellulose sulphate, PRO 2000®) provide a physical barrier that keeps HIV and other pathogens from reaching the target cells. Another class of microbicides (e.g. Acidform®, BufferGel® and Lactobacillus crispatus) act by enhancing the natural vaginal defence mechanisms by maintaining an acidic pH, which protects the vagina. C31G and octoxynol-9 kill or disable pathogens by stripping them of their outer covering. Another class of products e.g tenofovir (PMPA) acts by preventing replication of the virus after it has entered the cell. There are 23 microbicide products in various stages of clinical development. Carraguard®, a product of the Population Council, is in Phase III effectiveness trial in South Africa and Botswana. Phase II/III studies of BufferGel® and PRO 2000® are on-going in India, Malawi, South Africa, United Republic of Tanzania and Zimbabwe. Expanded Phase II studies are in progress for Carraguard, dextrin sulphate, Lactobacillus crispatus and PRO 2000®. Products that are in Phase I include Acidform®, C31G, cellulose sulphate, and tenofovir.
Nonoxynol-9 is a spermicide which has been in widespread use as a contraceptive for many years. It is available over-the-counter in different formulations (gels, suppositories and film) and can be used alone or as additional protection on top of condoms, diaphragms or other physical barrier methods.
Considerable research has been done on the safety and effectiveness of Nonoxynol-9 for HIV prevention. WHO, in collaboration with the CONRAD Program, convened a technical consultation in October 2001 to review the data on the use of Nonoxynol-9 as a spermicide.
Key conclusions from the technical consultation include:
Human Resources, Infrastructure and Supplies Needed
Distribution of microbicides will be influenced to a large extent by whether they are available for sale by prescription or over-the-counter (OTC). If an effective microbicide becomes available for use on the market as an OTC it can use the same distribution system as condoms. Their use can be advocated for in HIV/AIDS, STI, maternity and family planning clinics, and in youth or adolescent health care. Health care personnel working in this variety of settings can be trained in the use – and importance – of microbicides.
A recent cost-benefit analysis conducted at the London School of Hygiene and Tropical Medicine indicates that the introduction in 73 lower-income countries of a microbicide which reduced the risk of infection by 40%, at 30% coverage, would avert approximately 6 million HIV infections over 3 years in men, women and children (Charlotte Watts, personal communication). In addition, this would reduce the health care costs (excluding the cost of antiretroviral therapy) by a staggering 3.2 billion US dollars. This implies that a microbicide with relatively low-effectiveness could have a substantial impact against the global HIV epidemic if it were used by a significant number of women.