Acyclovir for Encephalitis How It Works Acyclovir prevents
herpes simplex virus—the virus that causes chickenpox, 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 treatment.1 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 altered conscio