Aciclovir is one of the most widely used antiviral drugs in the world. It was first available as a prescription drug in 1983, but deliberation for over-the-counter use began in 1994. It has since been marketed under trade names like Zovir and Zovirax. "Acyclovir" is its United States Adopted Name (USAN), though this was formerly its British Approved Name (BAN). The International Nonproprietary Name (INN) is spelled as "aciclovir."

The development of aciclovir was perceived as a milestone in antiviral therapy. In 1988, Pharmacologist Gertrude B. Elion was awarded the Nobel Prize in Medicine, in part for developing aciclovir. Unto now, this drug is prized for its high selectiveness and low toxicity to cells, or cytotoxicity. Aciclovir is considered a prodrug - a medication that is packaged in a virtually inactive form, but is metabolized into a more active form after it has been administered.

This drug is effective against most species of the herpesvirus family. It is most effective in Herpes simplex virus type 1 (HSV-1) - a viral condition that is commonly known as cold sores. Cold sores are characterized by blisters appearing around the mouth area or other parts of the face, although in rare cases it also appears on the gums or the hard palate of the mouth. They must not be confused with canker sores, which are non-infectious ulcers that temporarily appear on the soft tissues of the mouth. Cold sores usually last from 7 to 10 days.

This is an infection that more commonly attacks small children. Once it has entered the body, it settles in the brain and becomes dormant, resurfacing later in life. There is no cure for HSV-1, but it is possible to limit the duration of every episode, by applying topical forms of Aciclovir directly onto the afflicted parts of the face.

Genital herpes, or HSV-2, is also among the herpes viruses that can be inhibited with aciclovir. This virus may also cause a lifelong infection, with potential for recurrence. It may be transmitted through skin-to-skin contact, sexual contact, or through an exchange of saliva. An expectant mother who has been infected with genital herpes may pass on the ailment to the baby. A baby born with any form of herpes may face life-threatening health risks. Aciclovir may prevent the spread of the herpes virus on the skin or mucuous membranes of an infected adult, but a single round of treatments cannot completely prevent recurrences.

Chickenpox comes next in the succession of viral conditions against which aciclovir is effective. It is a highly infectious condition that is also known as Varicella simplex. This condition is caused by the varicella-zoster virus (VZV), one of the eight herpes viruses known to affect humans. This is recognizable by fever and the appearance of red spots all over the limbs and torso.

Chickenpox has an incubation period of 10-14 days, and is most contagious two days before symptoms appear. If a person has been immunocompromised, or has become especially vulnerable to malicious infections, chickenpox may pave the way to developing life-threatening complications. Intravenous aciclovir is recommended instead of oral aciclovir in such cases.

Intravenous preparations are more potent, but they also achieve higher blood levels. Liquid aciclovir is also administered to acute cases of herpes zoster, as well as encephalitis, or herpes infection of the brain. Newborn babies are far more susceptible to any viral infection, therefore intravenous administration of aciclovir to herpes-infected infants is often required.

Aciclovir is most effective during the first few days of a Herpes zoster infection. Examples of such an infection are shingles, which may appear during the onset of chickenpox, particularly among adults. It is evident that the older one gets, the more prone one is to contract Herpes zoster. Shingles were traditionally known as "St. Anthony's fire" because of its symptoms of fiery red blisters that appear on the torso.

Aciclovir may also be used in treating ocular herpes. This occurs when the HSV-1 targets the eyes, resulting in blurred vision, irritation, and sometimes scarring and blindness. As a product of the HSV-1 virus, this condition is not commonly sexually transmitted. There are several forms of ocular herpes, or eye herpes, which include the following: herpes keratitis, stromal keratitis, and iridocyclitis.