Does nonoxynol-9 protect against HIV?

Dear Cecil:

I hear the HIV virus is easily killed with the nonoxynol-9 spermicide. In your archives somewhere you said that the probability of contracting HIV during heterosexual sex from an HIV-infected person is approximately 1 in 500. How would those odds change if nonoxynol-9 were used?

Cecil replies:

One thing you learn about medicine is that it’s one-third science, one-third guess, and one-third hope like hell — and often it’s far from clear which third is which. I’m not saying this to kvetch; when you’ve got people begging you to save their lives, you do what you can do. But you do run the risk of occasionally having to eat your words. That’s what happened with nonoxynol-9 (N-9). Right now they’re saying yes, this once widely touted drug might change your odds of contracting HIV. But — and we’re really sorry about this — it might make them go up, not down.

N-9 was originally developed as a spermicide and is the only one currently approved for use in the U.S. It’s found in contraceptive foam, film, and diaphragm gel and in the lubrication used on some condoms. Then they found out in the lab that it kills gonorrhea, chlamydia, and HIV. About three-fourths of the sexual lubricants sold today contain it. These lubricants have become popular with gay men for use during anal sex, despite the lack of clinical evidence that this will prevent the spread of HIV or other sexually transmitted diseases.

Earlier this year researcher David Phillips reported at a federally sponsored conference that he’d tested N-9 on mice. It prevented transmission of herpes simplex when used vaginally, but when used rectally all the test animals died (herpes is fatal to mice), even when very small amounts of virus were used. You may be thinking what I’m thinking (“No, no, Igor, the N-9 goes in the mouse’s rectum, not the mouse in the …”), but we’ll trust Dr. Phillips knows what he’s doing. Anyway, on further investigation, “one biopsy of mouse rectal tissue looked like craters of the moon under a microscope,” according to an account in the Bay Area Reporter. The N-9 caused the surface cells to slough off, multiplying the possible routes for infection. A small-scale study (four subjects) in humans found a similar result — N-9 stripped off epithelial cells, potentially increasing the chances of STD transmission. N-9 is a “nonionic detergent” — you can find variants of it in degreasers sold at auto parts stores — so it’s not surprising that it might damage delicate tissue.

OK, we’re talking gay men and rodents here, but don’t get smug, Mr. and Mrs. Missionary Position. A number of studies of female prostitutes in Africa, where heterosexual transmission of HIV is common, have found N-9 confers little or no benefit. What’s more, a study of 20 South African female “sex workers” published in the fall 1999 issue of AIDS found that use of 72-milligram contraceptive film was linked to genital lesions and other side effects. The jury’s still out on this one, though; other studies haven’t found any problems with N-9 products when used vaginally.

What does seem clear is this: while N-9 isn’t necessarily doing you any harm, it probably isn’t protecting you from HIV, either. (See for a summary from the Centers for Disease Control.) Bottom line: to avoid HIV, be careful who you have sex with (or don’t have sex at all), use condoms, and don’t rely on spermicides alone.

Questions we’re still thinking about

Dear Cecil:

What does a fart look like in infrared? How about using Kirlian photography?

Silly creature. This is why God gave college students matches — because they couldn’t afford infrared film.

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