In the U.S.—

In Canada—

Another commonly used name is aciclovir.

• Antiviral, systemic

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)

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For acyclovir, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to acyclovir or valacyclovir. Also tell your health care professional if you are allergic to any other substances, such as foods, sulfites or other preservatives, or dyes.

Pregnancy—Acyclovir has been used in pregnant women and has not been reported to cause birth defects or other problems. However, studies have not been done in humans. Studies in rats and rabbits have shown that acyclovir given by injection may keep the fetus from becoming attached to the lining of the uterus (womb). However, acyclovir has not been shown to cause birth defects or other problems in mice given many times the usual human dose, or in rats or rabbits given several times the usual human dose.

Breast-feeding—Acyclovir passes into breast milk. However, it has not been reported to cause problems in nursing babies.

Children—A limited number of studies have been done using oral acyclovir in children, and it has not caused different effects or problems in children than it does in adults.

Older adults— Agitation, confusion, dizziness, and drowsiness may be especially likely to occur in elderly patients who are usually more sensitive than younger adults to the central nervous system effects of acyclovir.

Other medicines—Although certain medicines should not be used together at all, in many cases two different medicines may be used together even if an interaction might occur. In these cases, changes in dose or other precautions may be necessary. If you are taking acyclovir it is especially important that your health care professional know if you are taking any of the following:

• Carmustine (e.g., BiCNU) or
• Cisplatin (e.g., Platinol) or
• Combination pain medicine containing acetaminophen and aspirin (e.g., Excedrin) or other salicylates or
• Cyclosporine (e.g., Sandimmune) or
• Deferoxamine (e.g., Desferal) (with long-term use) or
• Gold salts (medicine for arthritis) or
• Inflammation or pain medicine, except narcotics, or
• Lithium (e.g., Lithane) or
• Methotrexate (Mexate) or
• Other medicine for infection or
• Penicillamine (e.g., Cuprimine) or
• Plicamycin (e.g., Mithracin) or
• Streptozocin (e.g., Zanosar) or
• Tiopronin (Thiola)—Concurrent use of these medicines with acyclovir may increase the chance for side effects, especially when kidney disease is present

• Dehydration or
• Kidney disease—Dehydration or kidney disease may increase blood levels of acyclovir, increasing the chance of side effects

• Nervous system problems—Acyclovir may make these problems worse

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.

Dosing—

The dose of acyclovir will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of acyclovir. Your dose may be different if you have kidney disease. If your dose is different, do not change it unless your doctor tells you to do so.

The number of capsules or tablets or teaspoonfuls of suspension that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are taking acyclovir.

• For oral dosage forms (capsules, oral suspension, or tablets):
  • For treatment of genital herpes:
    • Adults and children 12 years of age and older—200 milligrams (mg) five times a day for ten days.
    • Children up to 12 years of age—Use and dose must be determined by the doctor.
  • For prevention of recurrent outbreaks of genital herpes infections:
    • Adults and children 12 years of age and older—200 to 400 mg two to five times a day for five days or up to twelve months, depending on how often your outbreaks of infection occur.
    • Children up to 12 years of age—Use and dose must be determined by the doctor.
  • For treatment of chickenpox:
    • Adults and children who weigh over 88 pounds (40 kilograms)—800 mg four times a day for five days.
    • Children 2 years of age and older and weighing 88 pounds (40 kilograms) or less—Dose is based on body weight and must be determined by the doctor. The usual dose is 20 mg per kilogram (kg) of body weight, up to 800 mg, four times a day for five days.
    • Children up to 2 years of age—Use and dose must be determined by the doctor.
  • For treatment of shingles:
    • Adults and children 12 years of age and older—800 mg five times a day for seven to ten days.
    • Children up to 12 years of age—Use and dose must be determined by the doctor.
• For injection dosage form:
  • For treatment of herpes of the brain, genitals, or mucous membranes, or for the treatment of shingles:
    • Adults and children 12 years of age and older—Dose is based on body weight and must be determined by the doctor. The usual dose is 5 to 10 mg of acyclovir per kg (2.3 to 4.5 mg per pound) of body weight, injected slowly into a vein over at least a one-hour period, and repeated every eight hours for five to ten days.
    • Children up to 12 years of age—Dose is based on body weight and must be determined by the doctor. The usual dose is 10 mg to 20 mg of acyclovir per kg (4.5 mg to 9.1 mg per pound) of body weight, injected slowly into a vein over at least a one-hour period and repeated every eight hours for seven to ten days.
  • For treatment of widespread herpes virus infection in newborns:
    • Infants from birth to 3 months of age—Dose is based on body weight and must be determined by the doctor. The usual dose is 10 mg of acyclovir per kg (4.5 mg per pound) of body weight, injected slowly into a vein over at least a one-hour period and repeated every eight hours for ten days.

Missed dose—

If you do miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage—

To store this medicine:

• Keep out of the reach of children.
• Store away from heat and direct light.
• Do not store the capsule or tablet form of this medicine in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

If your symptoms do not improve within a few days, or if they become worse, check with your doctor.

The areas affected by herpes, chickenpox, or shingles should be kept as clean and dry as possible. Also, wear loose-fitting clothing to avoid irritating the sores (blisters).

It is important to remember that acyclovir will not keep you from spreading herpes to others.

Herpes infection of the genitals can be caught from or spread to your partner during any sexual activity. Even though you may get herpes if your partner has no symptoms, the infection is more likely to be spread if sores are present. This is true until the sores are completely healed and the scabs have fallen off. Therefore, it is best to avoid any sexual activity if either you or your sexual partner has any symptoms of herpes. The use of a latex condom (“rubber”') may help prevent the spread of herpes. However, spermicidal (sperm-killing) jelly or a diaphragm will probably not help.

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:

• 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 
  
  

• 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.

Once a medicine has been approved for marketing for a certain use, experience may show that it is also useful for other medical problems. Although not specifically included in product labeling, acyclovir by injection is used in certain patients with the following medical conditions:

• Herpes simplex (for prevention of repeated infections) in people with a weak immune system
• Herpes zoster infections of the eye
• Shingles (for prevention of repeated infections) in people with a weak immune system

Other than the above information, there is no additional information relating to proper use, precautions, or side effects for these uses.