Acyclovir is a medication commonly used to treat viral infections. It is most typically used for the treatment of genital herpes and herpes zoster (shingles). The brand name of acyclovir is Zovirax.

Acyclovir has an interesting structure and mechanism of action. It is a type of nucleoside analogue. Nucleosides are the basic building blocks of DNA. Acyclovir is very similar to these nucleosides, yet very subtly different. A virus will take up the drug and try to incorporate it in to it's DNA as it grows. However, when it does, the small differences in structure between the drug and a real nucleoside will cause the DNA to malfunction.

Also of note is that acyclovir is not active when it is first ingested. It is given in an inactive form and modified by a viral enzyme (protein) known as viral thymidine kinase. Once this modification takes place, the drug becomes active. Viral strains that have a mutation that lacks this particular enzyme makes that virus resistant to treatment with acyclovir.

Acyclovir was one of the first antiviral medications developed to treat herpes infections. Even today it remains one of the most commonly prescribed treatments, despite the development of other drugs in the same category. In addition to treatment of genital herpes, it is also used to treat oral herpes (cold sores) and shingles (caused by herpes zoster).

Rarely, it will be used to treat Epstein-Barr virus (EBV), which is the cause of mononucleosis. Lastly, it has been shown to be effective in the treatments of Cytomegalovirus (CMV). It should be noted that acyclovir is not highly effective against EBV or CMV and is not a first choice treatment for these infections.

Just as antibiotics are not effective against viral infections, acyclovir (or any antiviral medication) is not effective against any type of infection caused by a bacteria. It is important to note that acyclovir is not a permanent cure. It must be taken continuously for it to be effective, although many people will take it only when they are having an acute herpes outbreak.

Acyclovir can be given in several forms. Most common is the oral tablet which is used by many people to control and treat herpes infections. There is also a topical creme which is used on active herpes lesions. In a hospital, doctors have access to an intravenous form, which is typically used in severe infections where it is important to get a large amount of the drug in to a person in a short time.

Acyclovir is notable for being very well tolerated with minimal side effects. The most common side effects are nausea and vomiting. Diarrhea is also possible. The topical form can cause a localized rash at the side where the creme is applied. Also there are no specific known risks, acyclovir should not be taken if you are pregnant.

Acyclovir can only be prescribed by your doctor. If you have any questions about this drug, talk to your doctor.

Learn more about this author, Erich Rosenberger M.D..
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