Acyclovir (ay-SYE-kloe-veer) 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.

Acyclovir is used to treat the symptoms of chickenpox, shingles, herpes virus infections of the genitals (sex organs), the skin, the brain, and mucous membranes (lips and mouth), and widespread herpes virus infections in newborns. Acyclovir is also used to prevent recurrent genital herpes infections. Although acyclovir will not cure herpes, it does help relieve the pain and discomfort and helps the sores (if any) heal faster.

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.

Acyclovir is available only with your doctor's prescription, in the following dosage forms:

Oral
• Capsules (U.S.)
• Oral suspension (U.S. and Canada)
• Tablets (U.S. and Canada)

Parenteral
• Injection (U.S. and Canada)

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.

If you are using acyclovir oral suspension, use a specially marked measuring spoon or other device to measure each dose accurately. The average household teaspoon may not hold the right amount of liquid.

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.

If you are taking acyclovir capsules, tablets, or oral suspension, you should drink plenty of water to avoid becoming dehydrated.

Side Effects of Acyclovir

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur:

More common--For acyclovir injection only

• Pain, swelling, or redness at place of injection 

• 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 
  
  

• Frequency not determined
  • Bleeding or oozing from puncture sites or mucous membranes (bowel, mouth, nose, or urinary bladder), continuing;  blistering, peeling, or loosening of skin;  bluish coloring, especially of the hands and feet;  blurred vision;  bruising at the place of injection;  changes in facial skin color;  changes in vision;  clumsiness;  coughing;  decreased consciousness;  difficulty in breathing or swallowing;  dizziness or feeling faint, severe ;  fast heartbeat;  irritability ;  itching or skin rash;  large hive-like swelling on face, eyelids, lips, tongue, throat, hands, legs, feet, sex organs;  mood or mental changes;  muscle cramps, pain, or weakness;  pale skin;  red or irritated eyes;  sense of agitation or uneasiness;  shakiness and unsteady walk;  sores, ulcers, or white spots in mouth or on lips;  swelling of eyelids, face, feet, hands, lower legs or lips;  swollen, painful, or tender lymph nodes (glands) in neck, armpit, or groin;  unsteadiness or other problems with muscle control or coordination;  yellow eyes or skin 
  
  

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. However, check with your doctor if any of the following side effects continue or are bothersome:

• More common-- Especially seen with high doses
  • General feeling of discomfort or illness 
  
  

Less common-- Especially seen with long-term use or high doses

• Diarrhea;  headache 

• Frequency not determined
  • Burning, prickling, or tingling sensations;  drowsiness;  loss of hair 
  
  

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.