Acyclovir: Uses, Dosage & Side Effects

Acyclovir is most commonly used to control and prevent outbreaks of genital herpes, but may also be used to help combat chicken pox or the shingles virus.

Acyclovir is used to decrease the pain associated with sores and blisters. This medication can also assist in increasing the speed in which these blisters heal. This type of medication is an antiviral synthetic nucleoside analogue. While this type of medication stops the outbreak of a virus in an individual, it cannot stop the spread of a virus to others.

Indications and Usage

Acyclovir is sold under the brand name Zovirax. It can be used to treat blisters or sores associated with chickenpox, shingles or herpes. This medication may be prescribed to help prevent the outbreak of genital herpes, though it cannot help prevent the spread of this disease. In less common cases, acyclovir has been prescribed to assist those with eczema herpeticum, oral hairy leukoplakia or to help prevent those with HIV from contracting herpes. Acyclovir is available in liquid, tablet and capsule forms, all of which are to be taken orally. You may take this medication with or without food. Most doses are administered for 5-10 days, starting as soon as the symptoms begin. Those using this medication to manage herpes may be required to take this medication 2-5 times a day for up to one year.

You should try to take this medication around the same time every day. Do not make any adjustments to your medication, including continuing your prescription past the allotted time, without your doctor's instruction to do so. Those taking the liquid form of this medication will need to shake it well before consuming. You may wish to take water with this dose to help ensure that all of the medication has been consumed. Talk to your doctor if your symptoms do not appear to be getting better while you use acyclovir. If your symptoms have been eliminated, continue to take your medication through the full length of your prescription to help ensure that they will not return.

Acyclovir Dosage

Adults treating herpes will be given 200 mg five times a day for up to 10 days. Those using acyclovir as a preventative for genital herpes may have their doses increased up to 400 mg per day. Doses for herpes prevention may be continued for up to one year, or as needed when outbreaks occur. Adults treating chickenpox will take 800 mg per day in four divided doses for five days, while those treating shingles will be given 800 mg in five divided doses for ten days.

Children treating chickenpox will be given 20 mg for every kilogram of body weight in four divided doses for up to five days. Children under 2 should not use acyclovir. Children under 88 pounds (approximately 40 kilograms) that require the use of acyclovir for other treatments will need to consult with their doctor about the appropriate dosing size.

Decreased dosage is also recommended for those with decreased renal function. They may not be able to clear the drug properly. Elderly patients have an increased risk of developing renal failure while using acyclovir.

Acyclovir is in pregnancy category B which means that it is generally safe to use while pregnant, though there have not been satisfactory studies to confirm this. If you are using acyclovir to help treat genital herpes, you will need to talk with your doctor about the risk of passing this disease to your child, as well as the risks of using this medication while you are pregnant.


Usual Dosage

Special Dosage

Genital Herpes

200 mg in 5 divided doses for 10 days

Children under 12 will have a dose determined by their doctor

Herpes Prevention

200-400 mg in 5 divided doses for up to one year, or as infections occur

Children's doses will be determined by a doctor


800 mg in 4 divided doses for 5 days

Children 2 and older will receive 20 mg for every kilogram of body weight in 4 doses for up to 5 days


800 mg in 5 divided doses for 5-10 days

Children's doses to be determined by a doctor

Acyclovir Side Effects

Some side effects may occur while your body is getting used to having acyclovir in its system. These include a general feeling of discomfort or illness, diarrhea, headache, tingling, prickling or burning sensations on the skin, drowsiness, or loss of hair. These side effects should decrease and will eventually become eliminated as you continue to use your medication. Contact your doctor if these side effects do not stop over time.

If you have an emergency injection of acyclovir given, it is common to experience pain, swelling or redness at the injection site. Other common side effects of all forms of acyclovir include abdominal pain, decreased urination, and increased thirst, loss of appetite, nausea, vomiting, and unusual fatigue. Let your doctor know if any of these side effects occur so your doctor can determine if you require an alteration in your prescription.

Rare side effects of acyclovir include red spots on the skin, black, tarry stools, chills, fever, confusion, blood in the urine or stool, seizures, hallucinations, trembling, sore throat or unusual bleeding or bruising. Let your doctor know right away if you experience any of these side effects as they may be signs of a negative reaction to the medication.

Types of Side Effects


Common Side Effects

Pain, swelling, redness at place of injection

Uncommon Side Effects

Abdominal pain, decreased urination, increased thirst, loss of appetite, nausea, vomiting, unusual fatigue

Rare Side Effects

Red spots on the skin, black, tarry stools, chills, fever, confusion, blood in the urine or stool, seizures, hallucinations, trembling, sore throat or unusual bleeding or bruising

Side Effects During Adjustment Period

General feeling of discomfort, diarrhea, headache, burning, prickling or tingling sensation, drowsiness, loss of hair


Drugs known to negatively interact with acyclovir include tizanidine, varicella virus vaccine, fosphenytoin, phenytoin, and valproic acid. Let your doctor know about these or any other medications you take regularly to help avoid creating a combination that could react negatively with this dosage.

In some patients, certain foods may cause a negative reaction when paired with acyclovir. This will vary from patient to patient, and is not dangerous. If you notice a particular food making you uncomfortable when you take your prescription, avoid it until you are through using this medication. You should also avoid alcohol and tobacco as these are both known to interact negatively with acyclovir.



Diovan is used to manage high blood pressure. This medication is often prescribed in addition to other medications to manage your condition.

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