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Brand names:

Zovirax®, Sitavig®

Other names:

Aciclovir; ACV; Acycloguanosine

Often used for:

Viral infections

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What is acyclovir?

Acyclovir is an antiviral medication. It works to control illness due to certain viruses in patients with weak immune systems. It may be used for herpes simplex virus (HSV), varicella (chicken pox), herpes zoster (shingles), or cytomegalovirus (CMV). When applied to the skin, acyclovir may be used for cold sores and genital warts.

Acyclovir can cause tissue damage if it leaks from the vein during IV administration. Patients may have irritation and skin damage at the IV site. Let a caregiver know if there is burning during administration.

Patients receiving acyclovir may have regular tests including blood draws and urine tests to check blood counts and monitor liver and kidney function. Patients receiving acyclovir by IV will be monitored for neurotoxicity. Problems such as tremor, confusion, agitation, and changes in consciousness can happen, especially in patients who receive high doses or have decreased kidney function.

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May be taken as a tablet or capsule by mouth

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May be taken as a liquid by mouth

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May be given as a liquid into a vein by IV

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May be applied on the skin

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Possible side effects

  • Nausea and vomiting
  • Fatigue or weakness
  • Headache
  • Diarrhea
  • Skin irritation at the IV site or where applied to the skin
  • Rash, itching, hives
  • Dizziness
  • Feeling sleepy
  • Kidney problems
  • Liver problems

Not all patients who take acyclovir will experience these side effects. Common side effects are in bold, but there may be others. Please report all suspected side effects to your doctor or pharmacist.

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Tips for families

Be sure to discuss these and other recommendations with your doctor or pharmacist.

  • While taking this medicine, it is important to drink plenty of fluids. Patients should follow the care team’s instructions for appropriate fluid intake.
  • Patients should tell their doctor if they are pregnant or breastfeeding.
  • Finish all doses of the medicine as instructed by a doctor or pharmacist.

Acyclovir at home:

  • This medicine may make you dizzy or drowsy. Do not drive or do anything that could be dangerous until you see how this medicine affects you.
  • When taken by mouth, acyclovir may be taken with or without food.
  • Swallow tablets and capsules whole. Do not cut, crush, or chew.
  • Shake the liquid form of the medicine before use.
  • Acyclovir can be given by feeding tube. Follow the instructions given by your doctor or pharmacist.
  • Cream and ointment: Wash hands thoroughly before and after applying to the skin. Keep away from the eyes. Avoid rubbing the area. Use a glove to apply the ointment to prevent spread of infection to other areas.
  • Buccal tablets: A buccal tablet is in the mouth between the cheek and gum and allowed to dissolve over time. When taking acyclovir as a buccal tablet, place the rounded side of the tablet on the gum above the canine tooth on the same side as the cold sore. Hold the tablet gently in place gently at least 30 seconds to make sure it sticks. Do not swallow, chew, or suck the tablet. Allow to dissolve for at least 6 hours. You may eat and drink normally, but be careful not to make the tablet come loose.
  • 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 acyclovir at room temperature.
  • Do not use the medicine past the expiration date.
  • Follow instructions for safe storage and disposal.