Skip to Main Content

Welcome to

Together is a new resource for anyone affected by pediatric cancer - patients and their parents, family members, and friends.

Learn More



Brand names:


Other names:


Often used for:

Viral infections

clipboard icon

What is acyclovir?

Acyclovir is a type of antiviral medication. It controls certain viruses in patients with weak immune systems. It may be used to help treat or prevent herpes simplex virus (HSV), varicella (chicken pox), herpes zoster (shingles), or cytomegalovirus (CMV). When applied to the skin, acyclovir may be used to treat cold sores and genital warts.

This medicine may be given in the clinic, hospital, or at home. It is usually used along with other medicines.

Your care team will order certain tests to check blood counts and monitor liver and kidney function. Patients that get acyclovir by IV will be monitored for effects on the nervous system (neurotoxicity). Problems such as tremor, confusion, agitation, and changes in consciousness can happen, especially in patients who receive high doses or have reduced kidney function.

Acyclovir can cause tissue damage, blisters, or skin irritation if it leaks from the vein. Tell your care team if your child has pain, burning, redness, or swelling around the IV site.

tablet and capsule icon

May be given as a tablet or capsule by mouth

liquid dropper icon

May be given as a liquid by mouth

iv bag

May be given as a liquid into a vein by IV

liquid drop on hand icon

May be applied on the skin

exclamation mark in a circle icon

Possible side effects

  • Nausea or vomiting
  • Kidney problems
  • Tiredness or fatigue
  • Weakness
  • Skin irritation at the IV site or where applied to the skin
  • Mouth sores
  • Headache
  • Dizziness
  • Low blood pressure
  • Trembling
  • Confusion
  • Diarrhea
  • Low blood counts (This may increase the risk of infection.)
  • Liver problems

Not all patients who take acyclovir will have these side effects. Common side effects are in bold, but there may be others. Please report any symptoms or side effects to your doctor or pharmacist. Find more information on side effects.

family icon

Tips for patients and families

Be sure to discuss all questions and instructions with your doctor or pharmacist.

  • Tell your doctor or pharmacist if you start any new medicine while taking acyclovir.
  • Take all doses as instructed.
  • Make sure your child drinks plenty of liquids.
  • This medicine may make your child dizzy or drowsy. Do not let your child do anything that could be dangerous until you see how this medicine affects them.
  • If your child has severe or watery diarrhea, tell your doctor right away.
  • It is important that patients tell the care team if they are sexually active, pregnant, or breastfeeding.

Acyclovir at home:

  • When taken by mouth as tablets, capsules, or liquid, acyclovir may be taken with or without food. Take with food if stomach upset occurs.
  • Tablets and capsules: Tablets can be cut and crushed if needed. Do not open capsules for administration.
  • Liquid medicine: Shake well before use. Use the measuring device that comes with the medicine. The oral liquid can be given by feeding tube. Follow the instructions given by your care provider or pharmacist. Discard the liquid medicine after 10 days or after the expiration date on the label.
  • Ointment: For the topical ointment, apply a thin layer on the skin with a gloved hand to prevent spread of infection to other areas. Rub in gently. Wash hands thoroughly before and after applying to the skin. Do not take the ointment by mouth. Keep away from the eyes.
  • Antacids may decrease how well acyclovir works. Your child should not take antacids, such as Tums® or Mylanta®, 2 hours before or after taking this medicine.
  • Give a missed dose as soon as possible. If it is near the time for the next dose, skip the dose. Do not give 2 doses at the same time.
  • Store at room temperature.
  • Do not use the medicine past the expiration date.
  • Follow instructions for safe handling, storage, and disposal.