(RxWiki News) Taking antiviral therapy medications - even at high dosages - is not sufficient to prevent the spread of genital herpes, even when symptoms are not present.
Even if people with HSV-2 are taking antivirals and have no symptoms of the disease, they can still transmit the disease to their sexual partners, concludes a recent study.
"Know your partners' sexual history to avoid STDs."
The study, led by Dr. Christine Johnston, MD, University of Washington Virology Research Clinic in Seattle, looked at data from three antiviral drug trials involving the medications aciclovir and valaciclovir.
The study revealed that "shedding" of HSV-2 still occurs during treatment with these medications during "breakthrough episodes" that occurred at similar frequencies across the trial groups.
Genital herpes can cause ulcers in the skin, mouth, lips and genital area, but those who have it often do not show outward symptoms.
Yet, even without obvious symptoms, the infection can remain in the person's nervous systems and periodically flare up.
These flare-ups can cause new sores and are contagious to others whose skin comes into contact with the infected person's genital areas.
The researchers concluded that it is therefore necessary to find additional therapies for those with HSV-2 to prevent them from passing the virus to sexual partners.
The three separate trials investigated by the study involved 113 patients with genital herpes who collected four genital swabs each day. Each study period lasted four to seven weeks with a week in between each one.
One trial compared patients taking no medication with those taking a standard dose of aciclovir (400mg twice daily).
The other two trials compared patients taking different dosages of medications to suppress gentile herpes. One compared patients taking a standard dose of valaciclovir (500 mg daily) with those taking a higher dose (800mg three times daily).
The other compared the effects of using just one of the medications with using both: a high dosage of aciclovir (800mg three times daily) with a standard dose of valaciclovir, versus valaciclovir alone at 1000mg three times daily.
Those taking no medication shed the virus at a higher frequency and for a longer period of time than those who were taking antiviral therapy.
Those taking a standard dosage of valaciclovir had contagious flare-ups that lasted about three times longer than those with a high dosage of valaciclovir (10 hours compared to 3 hours).
Those taking the highest dosage of valaciclovir also had a 50 percent lower chance of passing on the infection than those who took a standard dose of the drug. Those with the highest dosage of valaciclovir also reported a higher frequency of headaches.
Those taking valaciclovir and high-dose aciclovir had about the same number of flare-ups during which they might infect others. So did those taking the two different dosages of valaciclovir.
The researchers discovered that 80 percent of the shedding episodes occurred when the patients did not exhibit any symptoms of the disease.
"Our finding supports the hypothesis that these antiviral drugs do not suppress the release of virions into the genital tract," the authors wrote. "The maximum benefit of shedding reduction has probably been reached for currently available antiviral drugs."
They said that current anti-HSV therapy can still help prevent symptoms from occurring as frequently for those with the disease. But more research into better options is necessary.
"Suppressive therapies with greater potency, including antiviral drugs or immunotherapy in the form of therapeutic vaccines, are needed to provide substantial public health benefits, such as prevention of HSV-2 transmission and HIV-1 acquisition and transmission," they concluded.
The study was funded by the National Institutes of Health and appears online in The Lancet. The valaciclovir for the study was donated by GlaxoSmithKline.
Lead author Johnson is a research investigator, and two other authors are consultants, for AiCuris, GmbH, which is developing HSV treatments.
Two authors, David Koelle and Amalia Magaret, are consultants for Immune Design Corp., and author Lawrence Corey is the head of the scientific advisory board for Immune Design Corp.
Corey and Koelle hold patents related to vaccine development for herpes. Koelle is also a consultant to Sanofi-Pasteur and Agenus for HSV-2 vaccines and works for Coridon, Vical and PATH for assessing possible HSV-2 vaccines.
Five authors declared no conflicts of interest.