Class Name(s):

• 8:18.32 Nucleosides and Nucleotides

Pronunciation:

• (ay sye' kloe veer)

Brand Name(s):

• Sitavig^®¶
• Zovirax^®¶; also available generically

Other Name(s):

• Acycloguanosine
• ACV

WHY is this medicine prescribed?

Acyclovir is used to treat viral infections like chickenpox, herpes zoster (shingles) and genital herpes (a sexually transmitted disease). Acyclovir is in a class of medications called antivirals. It works by stopping the spread of the virus in the body.

Acyclovir will not cure herpes infections and may not stop the spread of herpes virus to other people.

HOW should this medicine be used?

Acyclovir comes as a tablet, a capsule, and a suspension (liquid) to take by mouth. It is taken with or without food two to five times a day, starting as soon as possible after your symptoms begin. The length of your treatment depends on your condition. Take acyclovir at around the same time(s) every day.

Take acyclovir exactly as directed. Do not take more or less of it or take it more often or for a longer time than prescribed by your doctor.

Your symptoms should improve during your treatment with acyclovir. Call your doctor if your symptoms do not improve or if they get worse.

Take or use acyclovir until you finish the prescription, even if you feel better. If you stop taking acyclovir too soon or skip doses, your infection may not be completely treated or may become more difficult to treat.

Are there OTHER USES for this medication?

This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.

What SPECIAL PRECAUTIONS should I follow?

Before taking acyclovir,

• tell your doctor or pharmacist if you are allergic to this medication, any part of this medication, or any other medications, foods or substances. Tell your doctor or pharmacist about the allergy and what symptoms you had.
• tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
• tell your doctor if there is a possibility you may be dehydrated from a recent illness or activity, or if you have or have ever had problems with your immune system; human immunodeficiency virus infection (HIV); acquired immunodeficiency syndrome (AIDS); or kidney disease.
• tell your doctor if you are pregnant, plan to become pregnant, or are breastfeeding. If you become pregnant while taking acyclovir, call your doctor.
• if you are taking acyclovir to treat genital herpes, you should know that genital herpes can be spread through sexual contact even if you don't have blisters or other symptoms and possibly even if you are taking acyclovir. Talk to your doctor about ways to stop the spread of genital herpes and about whether your partner(s) should receive treatment.

What SPECIAL DIETARY instructions should I follow?

Drink plenty of fluids while you are taking or using acyclovir.

What should I do IF I FORGET to take a dose?

Take the missed dose as soon as you remember it and take any remaining doses for that day at evenly spaced intervals. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.

What SIDE EFFECTS can this medicine cause?

Acyclovir may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

• nausea
• vomiting
• diarrhea
• feeling unwell or tired

Some side effects can be serious. If you experience any of the following symptoms, call your doctor immediately or get emergency medical treatment:

• hives; rash; itching; difficulty breathing or swallowing; swelling of the face, throat, tongue, lips, or eyes; or hoarseness
• blistering or peeling skin
• rash, fever, swollen glands, or swelling of the face
• pale skin; unusual bruising or bleeding; decreased urination; blood in the urine; swelling of the legs, feet, or ankles; yellowing of the skin or eyes; shortness of breath; fever; headache; or unusual tiredness or weakness
• aggressive behavior; confusion; agitation; difficulty speaking; numbness; burning, or tingling in the arms or legs; temporary inability to move parts of your body; shaking hallucinations (seeing things or hearing voices that do not exist); shaking of a part of your body that you cannot control; loss of consciousness; or seizures

Acyclovir may cause other side effects. Call your doctor if you have any unusual problems while you are taking or using this medication.

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online (http://www.fda.gov/Safety/MedWatch) or by phone (1-800-332-1088).

What should I do in case of OVERDOSE?

In case of overdose, call the poison control helpline at 1-800-222-1222. Information is also available online at http://www.poisonhelp.org/help. If the victim has collapsed, had a seizure, has trouble breathing, or can't be awakened, immediately call emergency services at 911.

Symptoms of overdose may include the following:

• agitation
• seizures
• extreme tiredness
• loss of consciousness
• swelling of the hands, feet, ankles, or lower legs
• decreased urination

What should I know about STORAGE and DISPOSAL of this medication?

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom).

Keep all medication out of sight and reach of children as many containers are not child-resistant. Always lock safety caps. Place the medication in a safe location - one that is up and away and out of their sight and reach. http://www.upandaway.org

Dispose of unneeded medications in a way so that pets, children, and other people cannot take them. Do not flush this medication down the toilet. Use a medicine take-back program. Talk to your pharmacist about take-back programs in your community. Visit the FDA's Safe Disposal of Medicines website http://goo.gl/c4Rm4p for more information.

What OTHER INFORMATION should I know?

Keep all appointments with your doctor and the laboratory. Your doctor may order certain lab tests to check your response to acyclovir.

Do not let anyone else take or use your medication. Ask your pharmacist any questions you have about refilling your prescription.

Keep a written list of all of the prescription and nonprescription (over-the-counter) medicines, vitamins, minerals, and dietary supplements you are taking. Bring this list with you each time you visit a doctor or if you are admitted to the hospital. You should carry the list with you in case of emergencies.

^¶ This branded product is no longer on the market. Generic alternatives may be available.

This report on medications is for your information only, and is not considered individual patient advice. Because of the changing nature of drug information, please consult your physician or pharmacist about specific clinical use.

The American Society of Health-System Pharmacists, Inc. represents that the information provided hereunder was formulated with a reasonable standard of care, and in conformity with professional standards in the field. The American Society of Health-System Pharmacists, Inc. makes no representations or warranties, express or implied, including, but not limited to, any implied warranty of merchantability and/or fitness for a particular purpose, with respect to such information and specifically disclaims all such warranties. Users are advised that decisions regarding drug therapy are complex medical decisions requiring the independent, informed decision of an appropriate health care professional, and the information is provided for informational purposes only. The entire monograph for a drug should be reviewed for a thorough understanding of the drug's actions, uses and side effects. The American Society of Health-System Pharmacists, Inc. does not endorse or recommend the use of any drug. The information is not a substitute for medical care.

AHFS^® Patient Medication Information™ Copyright, 2026. The American Society of Health-System Pharmacists^®, 4500 East-West Highway, Suite 900, Bethesda, Maryland. All Rights Reserved. Duplication for commercial use must be authorized by ASHP.

Selected Revisions: April 15, 2026.