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Acyclovir (Zovirax)

  • Generic name: Acyclovir (ACV)
  • Trade names: Zovirax, Cyclovir, Lovir, Medovir
  • Drug class: Antiviral agent
  • Dosage Forms: 200 mg, 400 mg, 800 mg tablets;
    Cream 5%


Acyclovir (Zovirax) is used to treat infections caused by herpes viruses: genital herpes, herpes labialis (cold sores or fever blisters), herpes zoster (shingles), and chickenpox.

Acyclovir, an acyclic purine nucleoside analogue, suppresses the replication and spread of the virus to other cells. But acyclovir does not rid the body of latent herpesviruses, so it does not cure herpes.

Acyclovir for Herpes

Acyclovir is effective in reducing the severity of both the primary and recurrent herpes outbreaks. Acyclovir accelerates the healing of lesions, limits the duration and severity of outbreaks, and cuts down virus shedding period.

Chronic suppressive or maintenance therapy with Acyclovir is generally prescribed in case of frequent or severe recurrences. But even a few outbreaks can be psychologically distressing to some people.

Acyclovir suppressive therapy reduces the frequency of genital herpes recurrences by 80% in people with six or more outbreaks per year. Suppressive therapy also greatly cuts the risk of herpes transmission.

For the best results, acyclovir should be started during prodrome or erythema stage before blisters are visible. When the lesions are in the papule or vesicle stage, there is no benefit to starting oral acyclovir.

Zovirax 5% cream, applied directly on cold sores, decreases discomfort, healing time (by about 0.5-0.6 days), and the duration of hard crust. The benefits of topical Zovirax are seen regardless of whether treatment is initiated early during prodrome stage or late (papule or vesicle stage).

How effective is Acyclovir?

Acyclovir effectiveness in primary outbreak of genital herpes:

Symptom/sign Duration of symptoms/signs (days)
Without acyclovir With acyclovir*
Viral shedding 9 2
Time until all lesions are crusted 10 7
Time until all lesions are healed 16 10
Local pain 7 5
Constitutional symptoms 6 3

*--Dosage = 200 mg five times daily for 10 days, given within six days of lesion onset. Information from Mertz GJ, Critchlow CW, Benedetti J, Reichman RC, Dolin R, Connor J. Double-blind placebo-controlled trial of oral acyclovir in primary genital herpes simplex virus infection. JAMA 1984;252:1147-51.

Acyclovir alternatives

Valacyclovir (Valtrex) represents an excellent safe and effective alternative to its more traditionally prescribed parent compound, acyclovir. When convenience of dosing or compliance is of particular importance, Valacyclovir is more suitable in comparison to acyclovir. Valacyclovir is similarly effective for genital herpes and cold sores, and may be superior to acyclovir in the treatment of herpes zoster.

Denavir (pencyclovir) cream is an alternative to Zovirax cream in the treatment of cold sores. Penciclovir shortens time to crusting and reduces the number of lesions significantly better in comparison to acyclovir.

A new over-the-counter medicine called docosanol (Abreva) may help cold sores heal faster and reduce bothersome symptoms.

  • Schmid-Wendtner MH, Korting HC. Penciclovir cream--improved topical treatment for herpes simplex infections. Skin Pharmacol Physiol. 2004 Sep-Oct;17(5):214-8.

zovirax cream
  • Acyclovir is the oldest of the antiviral medications. It has been available since 1985 in pill form.
  • Acyclovir represents the only antiviral medication available for intravenous administration.

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