More about Microbicides

Microbicides for sexually transmitted diseases are pharmacologic agents and chemical substances that are capable of killing or destroying certain microorganisms that commonly cause human infection (for example, the human immunodeficiency virus).

Microbicides are a diverse group of chemical compounds that exert their activity by a variety of different mechanisms of action. Multiple compounds are being developed and tested for their microbicidal activity in clinical trials. Microbicides can be formulated in various delivery systems including gels, creams, lotions, aerosol sprays, tablets or films (which must be used near the time of sexual intercourse) and sponges and vaginal rings (or other devices that release the active ingredient(s) over a longer period). Some of these agents are being developed for vaginal application, and for rectal use by those engaging in anal sex.

Although there are many approaches to preventing sexually-transmitted diseases in general (and HIV in particular), current methods have not been sufficient to halt the spread of these diseases (particularly among women and people in less-developed nations. Sexual abstinence is not a realistic option for women who want to bear children, or who are at risk of sexual violence. In such situations, the use of microbicides could offer both primary protection (in the absence of condoms) and secondary protection (if a condom breaks or slips off during intercourse). It is hoped that microbicides may be safe and effective in reducing the risk of HIV transmission during sexual activity with an infected partner.

Most of the first generation microbicides were formulated as semi-solid systems, such as gels, tablets, films, or creams, and were designed to be applied to the vagina before every act of intercourse. However, vaginal rings have the potential to provide long-term controlled release of microbicide drugs. Long-acting formulations, like vaginal rings, are potentially advantageous since they could be easy to use, requiring replacement only once a month. This ease of use could prove very important to make sure that products are used properly.

In 2010, the International Partnership for Microbicides began the first study in Africa to test the safety and acceptability of a vaginal ring containing dapivirine. Drugs might also be administered systemically through injectable or oral formulations known as PrEP. Injectable formulations may be desirable since they could be administered infrequently, possibly once a month. It is likely, however, that such products would need to be monitored closely and would be available only through prescription. This approach also carries the risk of emergence of ARV-resistant strains of HIV.

The development of rectal microbicides is not as advanced as that of vaginal microbicides. One reason for this is that the rectum has a thinner epithelium, greater surface area and lower degree of elasticity than that of the vagina. Due to these factors, a microbicidal preparation that is effective when applied vaginally might have a different degree of effectiveness when applied rectally.

In January 2010, the National Institutes of Health awarded two grants totaling $17.5 million to the University of Pittsburgh to fund research into rectal microbicides. That research will include investigations into product acceptability of rectal microbicides with homosexual men ages 18 to 30 years old.