Health Library Acyclovir for EncephalitisFrom Healthwise

Acyclovir prevents herpes simplex virus—the virus that causes chickenpox (varicella-zoster), and some other viruses—from reproducing. The medicine is given in a vein (intravenous, or IV) when used to treat encephalitis caused by these viruses.

Acyclovir is used to treat encephalitis caused by herpes simplex and varicella-zoster.

To improve the chance of survival from herpes simplex encephalitis, acyclovir should be given as soon as the illness is diagnosed. The death rate from this form of encephalitis is less than 30% when prompt treatment is given, compared with 70% to 80% without prompt treatment.¹

Other factors that affect the success of treatment include the age of the person and the level of consciousness. Confusion and disorientation (altered consciousness) are signs of encephalitis. People under age 30 and those who have a normal level of consciousness have better results than people over 30 and those who have altered consciousness.²

The length of the illness also is important. In one study, the chance of survival in people who had encephalitis for four or fewer days increased from 65% to 100% after acyclovir treatment.³ However, even with treatment, serious mental and physical impairments can occur, such as paralysis, seizures, or hearing loss.

Side effects of intravenous acyclovir include:

• Inflammation at the injection site.
• Short-term increase in the creatinine level in the blood.
• Nausea and vomiting.
• Itching, rash, or hives.
• Anemia.
• Lightheadedness.
• Headache.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

Acyclovir is approved for treating herpes simplex encephalitis only in people over 6 months old.

Valacyclovir, an antiviral medicine, is approved by the U.S. Food and Drug Administration (FDA) for herpes zoster treatment. It is being studied as a treatment for herpes simplex encephalitis. Some health professionals are now using the medicine for this purpose as an unlabeled use.

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Citations

1. Jubelt B (2005). Viral infections. In LP Rowland, ed., Merritt's Neurology, 11th ed., chap. 24, pp. 175–210. Philadelphia: Lippincott Williams and Wilkins.

2. Roos KL, Tyler KL (2005). Meningitis, encephalitis, brain abscess, and empyema. In DL Kasper et al., eds, Harrison's Principles of Internal Medicine, 16th ed., vol. 2, chap. 360, pp. 2471–2490. New York: McGraw-Hill.

3. Whitley RJ, Gnann JW (2002). Viral encephalitis: Familiar infections and emerging pathogens. Lancet, 359: 507–514.

Author:	Amy Fackler, MA Debby Golonka, MPH	Last Updated: August 17, 2006
Medical Review:	Adam Husney, MD - Family Medicine W. David Colby IV, MSc, MD, FRCPC - Infectious Disease
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