A microbicide is a substance that can substantially reduce transmission of sexually transmitted infections (STIs) when applied either in the vagina or rectum. A microbicide could be produced in many forms, including gels, creams, suppositories, films, lubricants, or in the form of a sponge or a vaginal ring that slowly releases the active ingredient.

The word ‘microbicides’ refers to a range of different products that share one common characteristic: the ability to prevent the sexual transmission of HIV and other STI pathogens (a pathogen is the agent that causes an infection) when applied locally.

Microbicides are not yet available. Scientists are currently testing many substances to see whether they help protect against HIV and/or other STIs, but no safe and effective microbicide is currently available. Right now, there are over 30 product leads, including 10 that have proven safe and effective in animals and are now being tested on people.

A microbicide could prevent HIV and STIs by either killing or immobilising pathogens, blocking infection by creating a barrier between the pathogen and the cells of the vagina or rectum; or preventing the infection from taking hold after it has entered the body. Ideally, the product would combine these mechanisms for extra effectiveness.

Scientists hope that some of the microbicides being investigated will prevent pregnancy whereas some will not. It is important to have both non-contraceptive microbicides and ‘dual-action’ microbicides that prevent pregnancy and infection, so that women and couples can protect their health and still have children.

Microbicides, like all other experimental drugs, must go through a carefully controlled series of tests for safety and effectiveness in laboratories and humans before they can become available for general use. Women’s health activists and researchers are working closely together to ensure that the clinical testing of microbicides in humans is thorough and ethical. Many of the substances and mechanisms of action under investigation are already commonly used in over-the-counter products.

The microbicides field has been characterised by an unusual interplay between advocacy and research. The earliest articulations of the need for a woman-initiated prevention method came from women themselves rather than policymakers and scientists, unlike the call for HIV vaccines which came from scientists. This was long before most people working in the field of AIDS understood or appreciated the huge impact of the epidemic on women.

Virtually all microbicides research to date has been conducted by non-profit and academic institutions or small biotech companies. Studies are being funded by charitable foundations and government grants. Large pharmaceutical companies have not invested significantly in this field, primarily because microbicides are a classic ‘public health good’ which would yield huge benefits to society but for which the profit incentive to private investment is low.

For more information on microbicides please visit www. global-campaign.org. Microbicides 2008, the fourth biannual international conference on microbicides was held in Delhi in February 2008. For an update on the conference please visit www.microbicides2008.com