Acyclovir (Zovirax) Tablets

  • Generic name: Acyclovir
  • Brand names: Zovirax
  • Therapeutic class: Antiviral, Nucleoside analogue

What is Acyclovir used for?

  • Initial and recurrent herpes simplex infections (HSV-1 and HSV-2)
  • Herpes zoster (shingles)
  • Chickenpox (varicella-zoster)

Starting acyclovir promptly when tingling sensation first appears is very important, because the medication works only during active viral replication.

Acyclovir is NOT an antibiotic and is used to treat only Herpesvirus infections.

Acyclovir safety

Pregnancy category: B. Extensive experience with acyclovir supports its safety in pregnancy and lactation.

Prolonged use: Long-term use of acyclovir is not associated with serious side effects or cumulative toxicity2.

Persons with renal impairment should be monitored carefully. Acyclovir can crystallize in the renal tubules, leading to a creatinine elevation.

Strict contraindications

  • Hypersensitivity to acyclovir

Major drug interactions

  • Cyclosporine, nephrotoxic agents: increased risk of renal dysfunction and reversible CNS manifestations; use concomitantly with caution.
  • Probenecid and cimetidine inhibit the renal clearance of acyclovir.

No significant drug interactions have been reported3. You can take acyclovir with most of commonly used medications, including antibiotics, NSAIDs (e.g. ibuprofen, naproxen), benadryl.

Acyclovir and alcohol

Alcohol does NOT interact with acyclovir and does NOT decrease its effectiveness3.

How fast does Acyclovir work?

How quickly does Acyclovir work for herpes (HSV-1, HSV-2)?

Acyclovir works relatively quickly. However, as its main benefit is an acceleration of the healing and disruption of the HSV replication, you will NOT experience rapid improvement in severity of symptoms.

When used for an acute herpes outbreak, acyclovir shortens the duration of an outbreak by approximately 2 days, time to complete healing of lesions, and reduces viral shedding4. So, you should notice dramatic benefits on fourth day of proper treatment. Most favourable results are achieved when acyclovir is started early at the onset of prodromal symptoms.

Keep in mind: Zovirax cream, unlike oral tablets, can be started at any stage of an outbreak.

How quickly does Acyclovir work for shingles?

Most people experience alleviation of pain and less frequent formation of new lesions after three days of treatment5.

Is Acyclovir as good as Valtrex?

Valtrex costs more but does it work better than acyclovir?

Valacyclovir and acyclovir are equally effective and safe in herpes simplex virus infections1. The primary difference is how often you need to take them.

In the treatment of herpes zoster valacyclovir is superior to acyclovir.

Acyclovir alternatives

  • Valacyclovir (Valtrex)
  • Famciclovir (Famvir)
  • For patients with acyclovir hypersensitivity -- foscarnet or cidofovir.
  • Cases of acyclovir resistance -- foscarnet.


  • 1. Tyring SK, Douglas JM Jr, Corey L, Spruance SL, Esmann J. Arch Dermatol. 1998 Feb;134(2):185-91. PubMed
  • 2. Goldberg LH, Kaufman R, Kurtz TO, Conant MA, Eron LJ, Batenhorst RL, Boone GS. Long-term suppression of recurrent genital herpes with acyclovir. A 5-year benchmark. Arch Dermatol. 1993 May;129(5):582-7.
  • 3. Zovirax prescribing information. PDR. 59th Edition. Montvale, NJ: Thomson PDR, 2005, p. 1686-1688.
  • 4. Fiddian AP, Halsos AM, Kinge BR, Nilsen AE, Wikstrom K. Am J Med. 1982 Jul 20;73(1A):335-7.
  • 5. Huff JC, Bean B, Balfour HH Jr, Laskin OL, Connor JD, Corey L, Bryson YJ, McGuirt P. Therapy of herpes zoster with oral acyclovir. Am J Med. 1988 Aug 29;85(2A):84-9.
  • 6. Gerald G. Briggs, Roger K. Freeman, Sumner J. Yaffe Drugs in Pregnacy and Lactation, 6th edition. LWW
  • 7. Pasternak B1, Hviid A. Use of acyclovir, valacyclovir, and famciclovir in the first trimester of pregnancy and the risk of birth defects. JAMA. 2010 Aug 25;304(8):859-66. PubMed

Last updated: September, 2015

Advanced Consumer Info

acyclovir 800 mg

  • Pregnancy Category: B. No adverse effects in the fetus or newborn attributable to the use of acyclovir during pregnancy have been reported6. According to the 2010 large nationwide cohort study7, acyclovir use during first trimester of pregnancy was linked with an increased risk of major birth defects.
  • Breastfeeding: Acyclovir is considered compatible with breast-feeding by the American Academy of Pediatrics6.
  • Half-life:
    Children 1-12 years: 2-3 hours
    Adults: 3 hours
  • Mechanism of action: Acyclovir disrupts the process by which the virus makes copies of itself and spreads to other cells.
  • To be active, acyclovir must undergo phosphorylation. It is phosporylated to its monophosphate by a virus-encoded thymidine kinase. Acyclovir is activated only in the infected cells, and is active only against actively replicating viruses. It cannot eradicate the latent virus.