Which HSV-2 Antiviral Works Best?
Over the past 20 years, genital herpes vaccine candidates have approached the finish line, but have never scored a ‘prevention’ touchdown.
Which means there is still not a commercially available vaccine that can prevent Herpes Simplex Virus (HSV), known as genital herpes.
These disappointing research efforts are primarily due to the variability of Herpesviruses, of which there are over 100 types.
There are 2 types of Genital herpes, herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2).
Until there is an approved vaccine to prevent genital herpes, antiviral medications are available to provide ‘treatment’ for these viruses.
Antiviral therapy is not a cure for HSV-2, but these medicines can make living with herpes easier.
Even persons with first-episode herpes who have mild clinical manifestations can develop severe symptoms.
Therefore, all patients with genital herpes can receive antiviral therapy, says the CDC.
The Food and Drug Administration (FDA) has approved various medicines that are direct-acting, small molecules that inhibit a key enzymatic step in the HSV-2 replication cycle.
There are 3 medicines taken as a pill, that are commonly used to treat HSV-2:
- Acyclovir (Zovirax),
- famciclovir (Famvir),
- valacyclovir (Valtrex)
Additionally, intravenous acyclovir therapy should be provided for patients who have severe HSV disease or complications that necessitate hospitalization, says the CDC.
Although these new agents have proven efficacious in the treatment of herpes infections, there remains a need for medicines with higher potency, more rapid and durable antiviral action, more convenient dosing regimens.
And, most importantly, new antivirals need fewer and less severe side effects, says the CDC.
The pipeline for new herpes medicines has been expanding as candidates have evolved more rapidly due to improvements in chemical synthesis.
A promising treatment for HSV-2 named pritelivir has demonstrated in a recent clinical trial that it delivers greater viral suppression than current medicines.
Oral pritelivir, a small molecule helicase-primase inhibitor with a novel mode of action, is currently in a clinical phase 2 study, called PRIOH-1, in the U.S.A.
Pritelivir inhibits HSV replication, but at the helicase-primase complex, and does not require an activation step
In this double-blind, randomized crossover study of 91 adults with recurrent genital herpes, the percentage of genital swabs with HSV detected over 28 days was significantly lower during use of pritelivir than the use of valacyclovir (2.4% vs 5.3%).
Additionally, the frequency of shedding episodes was not found to differ by treatment.
But, the proportion of episodes lasting less than 24 hours was higher during receipt of pritelivir vs valacyclovir (87% vs 69%).
Related to these positive results, the FDA on August 01, 2017 granted Fast Track designation for oral pritelivir.
In summary, these researchers said, "If you have it, you can shed, and if you’re shedding, you’re infectious.”
Which means, to reduce the risk of herpes transmission, condoms, abstaining from sexual activities during outbreaks, and taking antiviral therapy are logical prevention steps.
But, the risk of transmission is still not zero.
The common misconception is that people who contract herpes are irresponsible, but that’s usually not the case.
- Genital HSV Infections
- Trial on Efficacy and Safety of Pritelivir Tablets for Treatment of Acyclovir-resistant Mucocutaneous HSV (Herpes Simplex Virus)
- Effect of Pritelivir Compared With Valacyclovir on Genital HSV-2 Shedding in Patients With Frequent Recurrences
- More On Vical's Herpes Vaccine: An Interview With Larry Smith, Ph.D.
- Genital Herpes Treatment and Care
- Safety and Efficacy Study of Herpes Simplex Virus Type 2 (HSV-2) Therapeutic DNA Vaccine (HSV-2)
- Candidate anti-herpesviral drugs; mechanisms of action and resistance
- Standard-dose and high-dose daily antiviral therapy for short episodes of genital HSV-2 reactivation
- Herpes-2 Vaccine Candidate Update