Generic name: acyclovir [ ay-SYE-kloe-vir ]
Brand name: Zovirax
Drug class: Purine nucleosides

Medically reviewed by Drugs.com. Last updated on Mar 29, 2024.

Uses for acyclovir

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.

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.

Before using acyclovir

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 this medicine, the following should be considered:

Allergies

Tell your doctor if you have ever had any unusual or allergic reaction to this medicine or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.

Pediatric

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.

Geriatric

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.

Breast Feeding

Studies in women suggest that this medication poses minimal risk to the infant when used during breastfeeding.

Interactions with Medicines

Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking this medicine, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using this medicine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

• Bupropion
• Dichlorphenamide
• Emtricitabine
• Fexinidazole
• Foscarnet
• Leflunomide
• Nitisinone
• Tenofovir Alafenamide
• Teriflunomide

Using this medicine with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

• Fosphenytoin
• Phenytoin
• Valproic Acid

Interactions with Food/Tobacco/Alcohol

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. Discuss with your healthcare professional the use of your medicine with food, alcohol, or tobacco.

Other Medical Problems

The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:

• 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.

Proper use of acyclovir

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.

Dosing

The dose of this medicine 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 this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine 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 using the medicine.

• 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 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

Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.

Keep out of the reach of children.

Do not keep outdated medicine or medicine no longer needed.

Precautions while using acyclovir

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.

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

Some 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. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

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 may also occur in some patients. If you notice any other effects, check with your healthcare professional.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Related/similar drugs

Commonly used brand name(s)

In the U.S.

• Zovirax

In Canada

• Acyclovir

Available Dosage Forms:

• Tablet
• Suspension
• Capsule
• Powder for Solution
• Solution

Therapeutic Class: Antiviral

Pharmacologic Class: Viral DNA Polymerase Inhibitor

Chemical Class: Guanosine Nucleoside Analog

Frequently asked questions

• Can you drink alcohol while taking acyclovir?
• What would be the benefits of taking valacyclovir vs acyclovir?

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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