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What is Acyclovir?

Karyn Maier
Updated May 17, 2024
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Acyclovir is an antiviral medication that is frequently prescribed to combat various strains of the herpes virus, most notably herpes simplex virus type I (HSV-1). Since the raw crystalline powder has the lengthy chemical name of 2-amino-1,9-dihydro-9-[(2-hydroxyethoxy)methyl]-6H-purin-6-one, it is most commonly referred to in clinical settings as acycloguanosine. However, it is marketed as a pharmaceutical under the trade names Cyclovir, Acivir, Zovirax, and Herpex, with Acyclovir being recognized as the standard International Non-proprietary Name for this drug.

The most common form of administering Acyclovir is in tablet, capsule, or liquid form, which may contain 200, 400, or 800mg of active ingredient. However, it may also be given by injection in 25mg/mL concentration to immunosupressed patients that are infected with varicella-zoster, the virus that causes chicken pox in children and shingles in adults. Acyclovir is also formulated into topical creams for the treatment of herpes simplex outbreaks affecting the mouth or genitals. In addition, the drug is available as an ophthalmic ointment or drops on a three percent concentration to treat keratitis of the cornea.

This drug’s ability to inhibit viral replication is due to it being highly selective toward thymidine kinase, an enzyme “programmed” by herpes simplex and varicella-zoster. This promotes a chain of enzymatic reactions and phosphorylation to bring about the conversion of Acyclovir to acyclovir monophosphate and ultimately to acyclovir triphosphate. The antiviral actvity triggered by these events can be observed both in vitro and in vivo, which means outside as well as inside the body, respectively. In addition, Acyclovir is a prodrug, meaning that it becomes active when introduced into the body in an inactive form and subsequently metabolized. This is fortunate since the drug is otherwise poorly absorbed.

While Acyclovir is well tolerated by most individuals, certain side effects have been reported with its use, most commonly nausea, headache, and diarrhea. Serious complications or allergic reactions are rare, but the medication should be discontinued immediately if visual disturbances or hallucinations are experienced, as well as seizure, elevated heartbeat, labored breathing, or swelling of the face or tongue. Acyclovir should not be taken while pregnant or nursing since the drug is known to merge into DNA and pass into breast milk. In addition, Acyclovir reacts with certain muscle relaxants and medications to treat gout, namely tizanidine (Zanaflex) and probenecid (Benuryl). Since this drug crystallizes in the kidneys, there may be a risk of kidney impairment following very high dosages given by injection.

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Karyn Maier
By Karyn Maier
Contributing articles to WiseGeek is just one of Karyn Maier's many professional pursuits. Based in New York's Catskill Mountain region, Karyn is also a magazine writer, columnist, and author of four books. She specializes in topics related to green living and botanical medicine, drawing from her extensive knowledge to create informative and engaging content for readers.
Discussion Comments
By amysamp — On Sep 15, 2011

@alFredo - Yes, I do know a couple of other sicknesses Acyclovir has been used to treat. One sickness Acyclovir has been used to treat is the measles virus; the other, autism.

When I read about the latter illness, autism, I was surprised to see they have even tried Acyclovir to try to treat it. Studies have found, for both measles and autism, that there is no link between the Acyclovir and the treatment of either.

In rare cases of both these diseases there seemed to be a correlation between Acyclovir with the treatment of measles and autism, but when looked at further it was found to be a mere coincidence.

By aLFredo — On Sep 14, 2011

A friend of mine is on a type of anti-viral medication that she just calls in whenever she has signs and/or symptoms of her virus. She says they have been very important to her safety and sanity. Once she takes the Acyclovir, she feels better and her symptoms go away within days.

Do you know any other well-known anti-viral medications that are on or have been in the market for these type of viral infections?

Do you know any other well-known ailments that Acyclovir has been known to treat?

By runner101 — On Sep 13, 2011

My father had a bad outbreak of shingles when he was in college, so he probably was given some form of Acyclovir. In his case, his shingles were already so bad that they left pock marks on his nose. Being a curious kid I asked him what was on his nose, and he tried to explain as best he could.

I am happy to hear that there is treatment for herpes, chicken pox, and shingles. I cannot and do not want to imagine people having to go through these sometimes reoccurring ailments without any relief.

Karyn Maier
Karyn Maier
Contributing articles to WiseGeek is just one of Karyn Maier's many professional pursuits. Based in New York's Catskill...
Learn more
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