Patient information about the treatment of herpes, chickenpox, or shingles is available with this medicine. Read it carefully before using this medicine. Acyclovir is best used as soon as possible after the symptoms of herpes infection or shingles (for example, pain, burning, blisters) begin to appear . If you are taking acyclovir for the treatment of chickenpox , it is best to start taking acyclovir as soon as possible after the first sign of the chickenpox rash , usually within one day. Acyclovir capsules, tablets, and oral suspension may be taken with meals or on an empty stomach. Acyclovir is best taken with a full glass (8 ounces) of water. To help clear up your herpes infection, chickenpox, or shingles, keep taking acyclovir for the full time of treatment, even if your symptoms begin to clear up after a few days. Do not miss any doses. However, do not use this medicine more often or for a longer time than your doctor ordered.

Acyclovir belongs to the family of medicines called antivirals, which are used to treat infections caused by viruses. Usually these medicines work for only one kind or group of virus infections.

Although not all of these side effects may occur, if they do occur they may need medical attention. Less common: Abdominal or stomach pain; decreased frequency of urination or amount of urine; increased thirst; loss of appetite; nausea or vomiting; unusual tiredness or weakness. Rare: Black, tarry stools; blood in urine or stools; chills, fever, or sore throat; confusion; convulsions (seizures); hallucinations (seeing, hearing, or feeling things that are not there); hives; pinpoint red spots on skin; trembling; unusual bleeding or bruising.

Acyclovir may also be used for other virus infections as determined by your doctor. However, it does not work in treating certain virus infections, such as the common cold.