Can You Avoid Genital Herpes By Taking Herpes Drugs?

Can PrEP strategy be used to prevent HIV work for herpes?

Woman Taking Pill
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Valtrex (valacyclovir), Zovirax (acyclovir), and Famvir (famciclovir) are three medications commonly used to treat genital herpes. People who have recurrent herpes will usually have them close at hand so that if the characteristic tingling and pain develops, they can start a course immediately and stave off or reduce the severity of an episode.

As the risk of transmission is highest when there are visible sores, it is important to prevent outbreaks to avoid passing the virus to others.

But, even if there are no visible symptoms, transmission can still occur. This is one of the challenges couples face when one partner has herpes and the other does not.

It is for this reason that some uninfected partners have taken to using Valtrex prior to sex, believing that doing so may reduce their risk of infection. It is a practice commonly known as pre-exposure prophylaxis (PrEP) in which a drug is used to prevent rather than treat an infectious disease.

It is a practice widely employed to prevent HIV, but do the same principles apply to herpes?

Understanding Pre-Exposure Prophylaxis

With HIV PrEP, the daily use of the drug Truvada (tenofovir plus emtricitabine) can reduce a person's risk of getting HIV by 90 percent or more. It does so by maintaining a high concentration of Truvada in the blood so that, if HIV does appear, the drug can quickly neutralize it at the site of exposure.

To make the strategy work, however, a person needs to take the drug on an on-going basis, ideally seven days per week.

There is some evidence, however, that men who have sex with men can achieve ample protection with as few as three doses per week. Women, on the other hand, may require near-perfect adherence to achieve the same level of protection. (Lab studies have shown that the drug is more available in rectal tissue than cervicovaginal tissues, explaining the disparity in protection.)

From the point of view of herpes, however, there has been little research on the pre-exposure benefits of anti-herpes drugs. This is due, in part, to the fact that herpes does not carry the same risk of death and illness as HIV. But does that alone explain why we haven't taken a more serious look at the prospect?

Challenges to Herpes Pre-Exposure Prophylaxis

As far back as 2003, the manufacturer of Valtrex conducted studies to assess whether the daily use of the drug by the infected partner would provide blanket protection to the uninfected person. What they found, unsurprisingly, was that, over a course of eight months, a daily 500 mg dose of Valtrex reduced the risk by 48 percent.

To date, however, no such study has been conducted to see if the same would happen if the situation were flipped, and the uninfected partner took Valtrex instead of the infected one. And the reason for this is simple: it would be unethical to do so. If the premise were to fail, the infected partner would have been unnecessarily placed in harm's way, and that would be wrong.

And, based on what we know about the drug, it would likely fail. For herpes PrEP to work, the drug would have to remain in the bloodstream at consistently high levels to provide a shield of protection, and that's where the model would likely fall apart.

It's simple math. Valacyclovir, acyclovir, and famciclovir each have a drug half-life of only 2.5 to 3.3 hours and an intracellular half-life of 10, meaning that it is expelled from the body very quickly. With Truvada, the drug half-life is 17 hours and an intracellular half-life of over 60. HIV PrEP works because the drug concentration remains stable for a long period of time between doses.

In order for Valtrex to do the same, a person would need to take multiple doses daily. Not only would this be impractical, it would be unnecessary given that condoms do provide some protection against genital herpes.

As a prevention tool, condoms are far from perfect, but they are more easy to adhere to than taking drugs each and every day.

HIV PrEP as Herpes PrEP?

Interestingly, scientists recently found that, within the construct of a committed relationship, persons taking HIV PrEP were 33 percent less likely to get genital herpes from an infected partner than those where weren't.

However, to achieve this benefit, the person would need to maintain near-perfect drug adherence, a task that is harder than it seems. As a practical solution to prevent herpes, irrespective of HIV, it would also be unrealistic given the risk of the long-term drug side effects (including kidney impairment and bone mineral loss).

With this in mind, the best way to avoid genital herpes is both basic and practical:

  • Use condoms consistently whether there are lesions are or not.
  • Limit your number of sex partners.
  • Avoid sex if there are any visible lesions or sores around the genitals, anus, or mouth.

Sources:

Bonnar, P. "Suppressive valacyclovir therapy to reduce genital herpes transmission: Good public health policy?" McGill J Med. 2009; 12(1):39-46. PMCID: PMC2687913.

Celum, C.; Morrow R.: Donnell, D. et al. "Daily oral tenofovir and emtricitabine-tenofovir preexposure prophylaxis reduces herpes simplex virus type 2 acquisition among heterosexual HIV-1-uninfected men and women: a subgroup analysis of a randomized trial." Ann Intern Med. 2014;161(1): 11-9. DOI: 10.7326/M13-2471.

Heinine, W. and Kashuba, A. "HIV Prevention by Oral Preexposure Prophylaxis." Cold Spring Harb Perspect Med. 2012; 2(3): a007419. DOI: 10.1101/cshperspect.a007419.

Magaret, A.; Mujugira, A.; Hughes, J. et al. "Effect of Condom Use on Per-act HSV-2 Transmission Risk in HIV-1, HSV-2-discordant Couples." Clin Infect Dis. 2016; 62(4):456-61. DOI 10.1093/cid/civ908.

Marcus, J.; Glidden, D.; McMahan, V. et al. "Daily oral emtricitabine/tenofovir pre-exposure prophylaxis and herpes simplex virus type 2 among men who have sex with men." PLoS One. 2014; 9(3):e91513. DOI: 10.1371/journal.pone.0091513.