What is Acyclovir?

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.