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Drug Halts Spread of Genital Herpes

Valacyclovir also reduces flare-ups, study finds

WEDNESDAY, Dec. 31, 2003 (HealthDayNews) -- An antiviral drug has been shown to help prevent the spread of herpes simplex virus 2, or genital herpes.

This finding, published in the Jan. 1 issue of the New England Journal of Medicine, led the U.S. Food and Drug Administration earlier this year to approve a new indication for the drug valacyclovir: to prevent genital herpes infection.

"That's an important new addition," says Dr. Clyde Crumpacker, author of an accompanying editorial in the journal and a professor of medicine at Harvard Medical School. "For the first time, it has been shown that the use of an antimicrobial can prevent transmission of a viral, sexually transmitted disease."

An estimated 22 percent of Americans have herpes simplex virus type 2 (HSV-2), the most common cause of genital herpes, with an estimated 1.6 million new cases acquired each year. According to Crumpacker, HSV-2 tends to recur six or more times a year.

Valacyclovir has already been shown to reduce flare-ups. "It's dramatically effective in preventing recurrences so [that is] the biggest use of this drug in the Western world," Crumpacker says. "Since genital herpes is the most common cause of ulcers in the genital area, there is widespread use for it."

Study author Dr. Larry Corey had already discovered that people with genital herpes often "shed" the virus without knowing it. "We showed that it occurred very frequently. In fact, the average person could shed 25 percent of the day and some people 50 percent and they were unaware of it," says Corey, head of the program in infectious diseases at Fred Hutchinson Cancer Research Center in Seattle. "Then we showed that the drug could reduce it from five out of 10 days to one out of 20. We also knew that most transmission occurred during these periods of asymptomatic shedding. Then the question we asked was could we interrupt the transmission of the infection from one person to the next."

Corey and his colleagues recruited 1,484 heterosexual, monogamous couples, one partner with herpes and one without. The partners who were infected with herpes were randomly assigned to receive either valacyclovir once a day or a placebo for eight months. All of the couples received counseling on safer sex and were offered free condoms on each visit to the clinic.

If the HSV-2-positive partners had a flare-up, they were given the option of treatment with valacyclovir for five days. After that, they resumed taking the randomly assigned medication.

Fourteen (1.9 percent) of the 743 negative individuals whose partners were taking valacyclovir became infected during the study period, compared with 27 (3.6 percent) of those whose partners were taking a placebo. Only four of the positive partners taking valacyclovir had a flare-up during the study period, compared with 16 of those on the placebo.

Valacyclovir reduced the transmission of HSV-2 by 48 percent and reduced recurrences by 75 percent.

The main reason for this is the drug reduced "shedding" of the virus. HSV DNA was detected in genital secretions on 2.9 percent of the days tested among HSV-2-infected individuals vs. 10.8 percent of the days of those on placebo.

It's not clear at this point how long a person would need to take the drug, Corey says.

These results were in addition to effects attributable to condoms or safe-sex counseling.

Using condoms is still an important protection, given that the lowest transmission rates were among those couples who almost always used condoms and when the source partner was taking valacyclovir.

"There has been a large avoidance of identifying people with genital herpes, but now you have a medical tool other than just condoms and abstinence," Corey says.

Also, because people with HSV-2 also have an increased incidence of HIV (human immunodeficiency virus) infection, especially in the developing world, the study findings may have larger implications. "This provides somewhat of a scientific basis [for estimating that] a drug to prevent or to decrease HSV-2 transmissions might also have a role in decreasing the spread of HIV-1 in the heterosexual population, where it's exploding," Crumpacker says.

The generic version of the drug is inexpensive, only about 20 cents a day or $73 a year, according to Crumpacker's editorial. And the therapy does not seem to induce resistance.

"This does provide a lot of hope for people with herpes," Crumpacker adds.

More information

For more on genital herpes, visit the National Institute of Allergy and Infectious Diseases or the American Social Health Association.

SOURCES: Larry Corey, M.D., head, program in infectious diseases, Fred Hutchinson Cancer Research Center, and professor, medicine, University of Washington, Seattle; Clyde Crumpacker, M.D., division of infectious disease, Beth Israel Deaconess Medical Center, and professor, medicine, Harvard Medical School, Boston; Jan. 1, 2004, New England Journal of Medicine
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