Herpes simplex antiviral therapy

, Associate Editor(s)-In-Chief: ; Lakshmi Gopalakrishnan, M.B.B.S.

Overview
There is no treatment that can cure herpes, but antiviral medications can shorten and prevent outbreaks during the period of time the person takes the medication. In addition, daily suppressive therapy for symptomatic herpes can reduce transmission to partners.

Mechanism of benefit

 * Antiviral medications used against herpes viruses work by interfering with viral replication, effectively slowing the replication rate of the virus and providing a greater opportunity for the immune response to intervene.
 * All drugs in this class depend on the activity of the viral enzyme, thymidine kinase, to convert the drug sequentially from its prodrug form to a monophosphate (with one phosphate group), diphosphate (with two phosphate groups) and, finally, triphosphate (with three phosphate groups) form that interferes with viral DNA replication.

Types of anti-viral medications

 * There are several prescription antiviral medications for controlling herpes simplex outbreaks, including aciclovir (Zovirax), valaciclovir (Valtrex), famciclovir (Famvir), and penciclovir.


 * Aciclovir was the original and prototypical member of this drug class and is now available in generic brands at a greatly reduced cost. Aciclovir is the recommended antiviral for suppressive therapy in the last months of pregnancy to prevent transmission of herpes simplex to the neonate.


 * Valaciclovir and famciclovir are prodrugs of aciclovir and penciclovir respectively, which have improved solubility in water and better bioavailability when taken orally. The use of valaciclovir and famciclovir, while potentially improving treatment compliance and efficacy, are still undergoing safety evaluation in this context. There is evidence in mice that treatment with famciclovir, rather than aciclovir, during an initial outbreak can help lower the incidence of future outbreaks by reducing the amount of latent virus in the neural ganglia. This potential effect on latency over aciclovir drops to zero a few months post-infection.

Antiviral treatment for Severe Disease:

 * IV acyclovir therapy should be provided for patients who have severe HSV disease or complications that necessitate hospitalization (e.g., disseminated infection, pneumonitis, or hepatitis) or CNS complications (e.g., meningitis or encephalitis).


 * The recommended regimen is acyclovir 5-10 mg/kg body weight IV every 8 hours for 2-7 days or until clinical improvement is observed, followed by oral antiviral therapy to complete at least 10 days total therapy.


 * Acyclovir dose adjustment is recommended for impaired renal function.

Side-effects
Allergic and other adverse reactions to acyclovir, valacyclovir, and famciclovir are rare. Desensitization to acyclovir has been described.