Killing or inactivating pathogens
Virucides disable the virus by breaking up its surface membrane or envelope or by inactivating key viral receptors or enzymes. If they are membrane-active compounds, they can also disable sperm, thereby acting as effective contraceptives. The challenge in this case is to make sure that virucides are specific enough to disrupt the invading pathogen, but without damaging the healthy cells that line the vaginal walls.
Strengthening the body’s normal defenses
This approach builds or improves upon what the body already does to protect itself. For example, a healthy vagina is normally acidic, which makes it inhospitable to invading pathogens like HIV. But semen counteracts this acidity, creating an environment where HIV can survive. Some candidate microbicides build on the simple principle of maintaining the vagina’s natural acidity even in the presence of semen.
Inhibiting viral entry
Entry inhibitors work by interfering with the virus getting into the body’s white blood cells, the target cells of HIV. There are two categories of entry inhibitors: attachment inhibitors that prevent attachment of the virus to white blood cells and fusion inhibitors that prevent HIV from actually entering cells.
Some candidate microbicides are being developed from the antiretroviral 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. If so, they could substantially lower the odds that the microbicide user will become infected.