What is a microbicide? The word “microbicide” refers to a range of different products that share one common characteristic: the ability to prevent the sexual transmission of HIV and other sexually transmitted infections (STIs) when applied topically. A microbicide could be produced in many forms, including gels, creams, suppositories, films, or as a sponge or ring that releases the active ingredient over time. Some microbicides may be active against sperm and act as contraceptives, while others could be non-contraceptive.
Microbicides are not yet available. Scientists are currently testing many substances to see whether they can prevent HIV and/or other STIs, but no safe and effective microbicide is currently available to the public. However, scientists are seriously pursuing almost 60 product leads, including at least eleven that have proven safe and effective in animals and are now being tested in people.
In March 2022, a silicone vaginal ring developed by the International Partnership for Microbicides (IPM) obtained approval from the South African Health Products Regulatory Authority. The ring releases the antiretroviral drug dapivirine over the course of one month and, although it does not involve a cervical barrier method, it could be the first microbicide with a localized effect to receive regulatory approval. Prior to approval in South Africa, the dapivirine ring was conditionally recommended by the World Health Organization in January 2021 and received a favorable opinion from the European Medicines Agency in July 2020. The World Health Organization reviewed the safety, quality, and efficacy of the method as compared to global standards. You can learn more about the next steps for the dapivirine ring here.
Microbicides and cervical barriers When a microbicide becomes available, cervical barriers may be appropriate candidates for delivery mechanisms and microbicide holders. If both products provide some degree of protection, using a microbicide together with a cervical barrier would likely enhance the protection offered. In addition, new products (such as the BufferGel cup) that combine microbicides and cervical barriers are already being developed and tested.
Mechanisms of action
HIV and STIs can attack the body in multiple ways, and an effective microbicide will help prevent infection by stopping this attack at one or more stages in the process. Most microbicides currently under development act in one or more of the following ways:
- Killing or inactivating pathogens. Some microbicides work by breaking down the surface or envelope of the virus or pathogen.
- Creating physical barriers. Gels or creams could provide a physical barrier between pathogens and vulnerable cells in the epithelium (cell wall) of the vagina or rectum.
- Strengthening the body’s normal defenses. The body has several naturally occurring defense mechanisms, such as the vagina’s natural acidity, that a microbicide may be able to supplement or enhance.
- Inhibiting viral entry. In order for HIV to infect a cell, particular viral proteins must bind themselves to matching receptors on the target cell’s membrane. Some candidate microbicides seek to interrupt this process by introducing other molecules that will bind with the receptors in advance, thus blocking the sites and preventing HIV attachment.
- Inhibiting viral replication. Some candidate microbicides are being developed from the anti-retroviral drugs that HIV positive people use to lower the amount of virus in their bodies. Formulated as gels or creams, these drugs may be able to suppress replication of any HIV that enters the vagina or rectum during sex.
For more information on microbicides, visit the websites maintained by the following organizations:
- AVAC Global Advocacy for HIV Prevention
AVAC maintains a microbicide research and development database with a list of products in the pipeline, clinical trials, supportive research.
- Global Campaign for Microbicides (Archived)
The Global Campaign led efforts to raise public awareness and mobilize political support for microbicides. Their website includes an archive of downloadable materials for advocates.
- International Partnership for Microbicides
IPM focuses on product development, capacity building at clinical trial sites, establishing regulatory pathways for microbicides, and planning for distribution.