How It Works
herpes simplex virus—the virus that causes
cold sores, and
genital herpes—from reproducing. The medicine is given
in a vein (intravenous, or IV) when used to treat
encephalitis caused by these viruses.
Why It Is Used
Acyclovir is used to treat
encephalitis caused by herpes simplex and varicella-zoster.
How Well It Works
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
The main things that affect
the success of treatment include the age of the person and his or her level of
consciousness. Confusion and disorientation (altered consciousness) are signs
of encephalitis. People younger than age 30 and those who have a normal level of
consciousness have better results than people older than 30 and those who have
People who get treatment with acyclovir immediately (within 4 days of symptoms) do better than people who wait longer for treatment.3 But even with treatment, serious mental
and physical impairments can occur, such as paralysis, seizures, or hearing
All medicines have side effects. But many people don't feel the side effects, or they are able to deal with them. Ask your pharmacist about the side effects of each medicine you take. Side effects are also listed in the information that comes with your medicine.
Here are some important things to think about:
- Usually the benefits of the medicine are more important than any minor side effects.
- Side effects may go away after you take the medicine for a while.
- If side effects still bother you and you wonder if you should keep taking the medicine, call your doctor. He or she may be able to lower your dose or change your medicine. Do not suddenly quit taking your medicine unless your doctor tells you to.
Common side effects of this medicine include:
- Pain, swelling, or redness where you got the shot.
- Belly or stomach pain.
- Nausea or vomiting.
See Drug Reference for a full list of side effects. (Drug
Reference is not available in all systems.)
What To Think About
Other antiviral medicines that may be used to treat encephalitis include valacyclovir, penciclovir, and
Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor if you are having problems. It's also a good idea to know your test results and keep a list of the medicines you take.
Complete the new medication information form (PDF)(What is a PDF document?) to help you understand this medication.
Jubelt B (2010). Viral infections and postviral syndromes. In LP Rowland, TA Pedley, eds., Merritt's Neurology, 12th ed., pp. 156–185. Philadelphia: Lippincott Williams and Wilkins.
Roos KL, Tyler KL (2008). Meningitis, encephalitis,
brain abscess, and empyema. In AS Fauci et al., eds, Harrison's Principles of Internal Medicine, 17th ed., vol. 2, pp. 2621–2641. New
Ropper AH, Samuels MA (2009). Acute encephalitis section of Viral infections of the nervous system, chronic meningitis, and prion diseases. In Adams and Victor's Principles of Neurology, 9th ed., pp. 716–723. New York: McGraw-Hill.
Primary Medical Reviewer
||E. Gregory Thompson, MD - Internal Medicine
Specialist Medical Reviewer
||W. David Colby IV, MSc, MD, FRCPC - Infectious Disease
||October 26, 2011