Herpes Antiviral Medications
What is Herpes?
Herpes is an infection caused by herpes simplex virus. It is caused by two viruses: herpes simplex virus type 1 (HSV-1), and herpes simplex virus type 2 (HSV-2).
HSV-1 virus usually is responsible for oral infections (cold sores), and can be transmitted through oral secretions. HSV-2 virus causes the majority of genital herpes cases and can be transmitted through oral or genital secretions.
However, lesion location does not necessarily indicate the type of virus.
Oral herpes (also called cold sores or fever blisters) is usually caused by herpes simplex virus 1. It usually affects the lips or mucous membranes in the mouth. Sometimes blisters appear in the nose and on cheeks.
Genital herpes is a chronic, life-long sexually transmitted infection. It is caused by the herpes simplex viruses type 1 (HSV-1) or type 2 (HSV-2). Most genital herpes is caused by HSV-2.
Medications for herpes infections
Currently, there is no cure for herpes. However, there are three antiviral medications approved by the Food and Drug Administration (FDA) for the treatment of herpes: acyclovir (Zovirax), famciclovir (Famvir) and valacyclovir (Valtrex).
Antiviral medications are used to prevent or treat herpes infections. They stop the growth of the herpes simplex virus. Antiviral medications may significantly lessen the severity of a primary outbreak and reduce the time it takes for genital herpes outbreaks to heal. The medication also decreases the number of days of painful symptoms and for some people, the number of days they can spread the virus.
According to the research data, the effectiveness of the acyclovir (Zovirax), famciclovir (Famvir), and valacyclovir (Valtrex) is equal. These drugs differ in their chemical structure, dosage regimen, cost and FDA licensed indications.
How do herpes antivirals work?
All three drugs disrupt the process by which the virus makes copies of itself and spreads to new cells. They do this by inhibiting an enzyme that the virus has but human cells do not and then interrupting the viruses' ability to synthesize DNA. None of the medicines cures the viral infection. Herpes virus will remain dormant in the body in the nerve ganglia.
Effectiveness of antiviral medications
The discovery of acyclovir was important breakthrough in medicine. Acyclovir, the first successful synthetic nucleoside analogue, was originally licensed in 1982 for the treatment of herpes and marketed under the brand name Zovirax®. Now this medicine is available as a generic from many manufacturers and is by far the cheapest of the available antiviral drugs.
Acyclovir is a safe and extremely well-tolerated.
The Acyclovir in Pregnancy Registry has documented prenatal exposures in more than 850 women (with 578 first-trimester exposures) without any adverse outcomes. However, the total number of pregnancies monitored to-date may not be enough to detect defects that occur only infrequently.
The topical form of acyclovir (Zovirax ointment) offers little benefit in the treatment of genital herpes and is not recommended. Zovirax ointment is used for the treatment of cold sores.
Valacyclovir, a new antiviral, is a prodrug converted to acyclovir in the intestine and liver. It has an oral bioavailability three to five times greater than that of acyclovir, allowing less frequent dosage regimen.
Valtrex, when taken daily (suppressive therapy) by a person with recurrent genital herpes, can reduce the risk of transmission to a partner. According to the scientific research3, valaciclovir (500 mg taken once daily) significantly reduces the rate of virus transmission:
Famciclovir (Famvir) is the oral form of penciclovir, a purine analog. The drug is quickly converted to its active form. Mechanism and efficacy are similar to those of acyclovir.
Famciclovir is effective for both episodic and suppressive therapy of genital herpes. Different dosages are used for different treatment goals.
Famciclovir, despite its favorable intracellular pharmacokinetics, must be given twice daily to be effective.
Animal studies4 found that famciclovir is superior to valacyclovir in reducing the establishment of HSV-1 latent infection.
A large volume of research suggests that the medications are safe and have only few side effects. They have never been noted to cause any long-term side effects.
All three antivirals are categorized as Pregnancy Category B.
All these drugs can have renal toxicity, and their dosage schedules must be reduced in patients with renal failure.
Last updated: April, 2011