New Class of Drug Shows Promise in the Treatment of Herpes

Genital herpes, one of the most common sexually transmitted infections, remains incurable. But now, newly published findings suggest one of the most promising experimental herpes- treatments in decades can significantly reduce the virus' ability to replicate and spread, and do so without the side-effects of current therapies

Above: TEM micrograph of a herpes simplex virus | Via Wikimedia Commons

The preliminary investigation – the results of which are published in the latest issue of the New England Journal of Medicine – sought to test the effectiveness of an experimental drug called pritelivir, by monitoring its ability to curb viral shedding in people with genital herpes. Viral shedding can occur even in the absence of physical symptoms of herpes simplex virus 1 and 2 (HSV-1 and 2), the two major members of the herpes family that infect humans. That the virus is transmissible, even in the absence of visible or otherwise noticeable symptoms, is one reason herpes is so common, affecting an estimated 50-million Americans, alone. Novel therapies like pritelivir show promise in their ability to not only decrease the length of time the virus is active, but also shrink the time window during which the infection is transmissible to sexual partners of people carrying the STI via viral shedding.

In the study, which the researchers admit was limited in size and duration, 156 HSV-2–positive test subjects were administered one of four doses of oral pritelivir for 28 days:

1. 5 mg/day

2. 25 mg/day

3. 75 mg/day

4. 400 mg, once-per-week

Swabs for HSV-2 testing were taken from the test subjects' genital areas daily, and participants maintained a diary of viral symptoms. The researchers describe their results:

HSV shedding among placebo recipients was detected on 16.6% of days; shedding among pritelivir recipients was detected on 18.2% of days among those receiving 5 mg daily, 9.3% of days among those receiving 25 mg daily, 2.1% of days among those receiving 75 mg daily, and 5.3% of days among those receiving 400 mg weekly.

In other words, pritelivir was shown to be effective in a dose-dependent fashion; the more of the drug people took, the lower their rate of HSV shedding. The 400 mg/week dose, while less effective than the 75 mg daily dose, might be easier to administer, or for people to remember, than a daily pill. The authors continue:

The percentage of days with genital lesions was also significantly reduced, from 9.0% in the placebo group to 1.2% in both the group receiving 75 mg of pritelivir daily (relative risk, 0.13; 95% CI, 0.02 to 0.70) and the group receiving 400 mg weekly (relative risk, 0.13; 95% CI, 0.03 to 0.52). The rate of adverse events was similar in all groups.

"This study represents a major a step forward in herpes research," said Dr. Stephen Tyring, a professor of dermatology at the University of Texas Health Science Center at Houston and coauthor of the study, in an interview with the Houston Chronicle. "The drug is still a few years from the market, but it should be a boon to the many people for whom existing therapy [like valacyclovir and acyclovir] has lost effectiveness."

The study is published in the New England Journal of Medicine. For more general information, visit US News & World Report and The Houston Chronicle. More on helicase-primase inhbitors (the class of therapies to which pritelivir belongs) at MedScape.