What is a Microbicide?

A microbicide is one of a number of substances that have the ability to kill or weaken microorganisms, including viruses, bacteria, or fungi. The main groups of microbicides are bactericides, fungicides, and viral microbicides. Bactericides in turn can be subdivided into disinfectants, used on inanimate objects, antiseptics, used externally on humans and animals, and antibiotics, which usually work internally.

The term microbicide is very often used to refer specifically to topical microbicides designed for the prevention of various sexually transmitted diseases. These microbicides are typically substances that can be applied internally to the vagina or rectum in the form of gels, creams, suppositories, or douches. They may also take the form of a sponge or other device that is inserted into the vagina or rectum, and that releases the microbicidal substance slowly over a period of time. Such microbicides may be designed as the primary protective mechanism against disease, or as an additional form of protection in case a condom should leak or come off during intercourse.

There are a number of different mechanisms by which microbicides may kill or harm microorganisms. Some types of microbicides disrupt the outer cell membranes of bacteria and viruses. The cell membranes are made out of lipids, and if the membrane is damaged then water can seek into the cell of the microorganism and kill it. These kinds of microbicides are termed detergent microbicides, or surfactants, and have the disadvantage that they often harm healthy human cells as well as the microorganisms they are designed to protect against.

There are a number of other microbicide mechanisms; one of these is the action of changing the pH of the host environment, typically the female vagina, to make it more alkaline, and thus make it a more hostile environment for microorganisms. Some microbicides, called replication inhibitors, prevent viruses from reproducing. Others, known as entry inhibitors or fusion inhibitors, stop viruses and bacteria from adhering to the human cells that they are attempting to attack.

Microbicide development often involves research into creating substances that combine two or more different anti-microbial actions in a single medication. Research into microbicidal action is of great interest to scientists studying the Human Immunodeficiency Virus (HIV). Microbicide trials suggest that even if a microbicide can reduce HIV infections by a modest percentage, if the substance were widely used, then a large number of new HIV infections could be prevented.