Image: Courtesy of Karl Malcolm
SAFETY RING: This X-ray image depicts the position of the silicone intravaginal ring in vivo.

When researchers learned that the spermicide nonoxynol-9 (N9) killed HIV in vitro, they were hoping that they had a cheap, ready-made, effective topical microbicide that women could use to block sexual transmission of HIV. But clinical trials showed that N9 increased vulnerability to HIV infection because it damaged mucosal cells, making the mucous membrane more permeable to the virus.1

This disappointment, however, did not discourage researchers from investigating topical microbicides, which are designed to prevent transmission of bacterial or viral infections; in this case, HIV or other sexually transmitted diseases. Moreover, such products would not be expensive, would be sold over the counter, and women would control their use: The less detectable the microbicide, the better the odds that women will use it. So, researchers turned to other substances...

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