About microbicides against HIV/AIDS
What are microbicides and how do they work?
Microbicides are compounds that can be applied directly to the vagina or rectum prior to sexual intercourse in order to prevent the transmission of HIV. They can come in the form of a gel, cream, or in a slow release device.
To date, no microbicide has been approved for use but there is a considerable research effort worldwide to develop microbicides. Microbicides that are under development can be broadly grouped; there are those that prevent attachment or entry of the virus to host cells or those that inhibit early stages of infection inside the host cell. CHAARM aims to develop microbicides from both groups and to investigate the use of combinations of microbicides to combat infection. Combinations of microbicides could have the advantage of being effective against some types of HIV that might be resistant to one of the individual microbicides.
Why do we need them?
The vast majority of new HIV infections are through sexual contact; therefore, the key to slowing the HIV epidemic is to prevent sexual transmission of HIV.
Condoms remain the most effective way of stopping sexually transmitted HIV; however, despite widespread efforts to encourage condom use many people do not have the power to avoid sexual contact with partners who may be HIV infected or to insist on condom use. This is particularly the case for women who may not have the ability to control their sexual interactions with men and safeguard their own sexual health. Microbicides have the potential to give more power to individuals to protect themselves against HIV.
The fact that microbicides could have a dramatic impact on HIV transmission is indicated by epidemiological modeling performed by the London School of Hygiene and Tropical Medicine. This modeling has indicated that a microbicide that is 60% effective could avoid up to 2.5 million infections worldwide over three years even if it is only used by a moderate number of people (for example if 20% of people who are in contact with local services in 73 low income countries used a microbicide 50% of the time that a condom is not used).
What are their features?
Microbicides have the potential to deliver many advantages in the battle against HIV transmission. The following list highlights some of the key features of microbicides:
- Microbicides could be formulated as creams, gels or sustained release formulations.
- Microbicides may act by disrupting intact HIV or by stopping HIV from attaching to host cells, entering or replicating in host cells.
- Microbicides could be used by an individual without the knowledge or cooperation of their sexual partner.
- Microbicides may be able to protect against other STI's as well as HIV - an advantage when considering that the presence of STI's increases an individual's risk of infection by HIV upon exposure to HIV.
- Microbicides may prevent the transmission of HIV from mother to unborn child.
- Ideally, microbicides could be provided in spermicidal and non-spermicidal forms, this means that a woman can protect herself from HIV infection yet still be able to decide if she wishes to allow pregnancy.
- There is the potential to formulate several drugs that act in different but complementary ways in a single microbicide therapy.
- Microbicides could be used anally as well as vaginally and hence be useful for sexual interactions between men as well as for women who engage in anal sex.
The future vision is that neither condoms nor microbicides will stand alone as options for HIV prevention. Instead they will form part of the growing arsenal of treatments and strategies designed to combat HIV infection and disease.