Acyclovir: Uses, Side Effects, Dosage, Precautions, and More

Medically Reviewed
Priyank Pandey
Written by Priyank Pandey on February 25, 2022Medically Reviewed by Kelly Johnson-Arbor, MD, Param Patel

About | Uses | Who can and can not take it? | How should it be taken? | Side effects | Precautions | Interactions | Missed dose | Overdose | Pregnancy | Breastfeeding

Generic name: Acyclovir or Aciclovir
Brand names:  Zovirax
Drug classes: Antiviral
Available forms: Capsule, tablet, oral suspension, and cream formulations

Acyclovir is an antiviral medication used to treat multiple viral infections including herpes, shingles, and chickenpox.

Uses

Aciclovir is used for the treatment of herpes simplex virus infections (cold sore, genital herpes), chickenpox and shingles. It may also be used for viral prevention purposes in immunocompromised patients that are undergoing chemotherapy or transplant recipients. The Intravenous form of aciclovir is used in hospitals for herpes simplex virus or varicella-zoster virus infection of the central nervous system. Aciclovir cream or ointment is used for cold sore treatment.

Who can and can not take it?

Many people can safely take acyclovir.

For people that have chronic kidney disease and worsened renal function or are on dialysis, the dose should be adjusted. 

Oral formulations of this drug have not been studied extensively in children younger than 2 years of age, so consult with your doctor or pharmacist about oral formulations for children.

Any person who has an allergy to aciclovir, valaciclovir or any of the ingredients in the formulation should avoid taking it. Acyclovir may interact with some other prescription medications, so check with your doctor or pharmacist about potential drug interactions before you start taking acyclovir.

How should it be taken?

Oral aciclovir can be taken with or without food. If using the oral suspension, shake well before use. Patients should drink plenty of fluids while taking acyclovir.

Acyclovir should be taken as prescribed. The dose of acyclovir depends on the condition it is being used for. In some cases, acyclovir is taken multiple times a day in doses of 800 mg at a time.

Side effects

Common side effects are nausea, vomiting, headache and diarrhea; taking aciclovir with food can help manage this.

Aciclovir can form crystals in the kidney and cause acute kidney injury, risk is higher in patients using the intravenous formulation and higher doses. If you have signs of kidney problems such as a change in the amount of urine, unusual back/side pain, speak to your doctor right away. Drinking plenty of fluids and staying well hydrated can help prevent this side effect.

It may rarely cause a life-threatening disorder that may affect blood cells, kidneys and other organs. Seek immediate medical attention if you develop confusion, agitation, lethargy, hallucination, dizziness/drowsiness, loss of consciousness, tremors or seizures. 

Seek immediate medication attention if there are any symptoms of an allergic reaction such as a rash, hives, dizziness, trouble breathing or swelling of face/lips/tongue/throat.

Precautions

Tell your doctor or pharmacist if you have kidney problems or you are an elderly patient, as the dose may need to be adjusted. Aciclovir does not protect against spreading genital herpes. Avoid sexual contact if you are having a flare.

Interactions

There are no significant drug interactions with aciclovir.

However, acyclovir is eliminated from the human body by the kidneys. Drugs that affect kidney function may alter levels of acyclovir within the body.

Missed dose

If you miss a dose, take it as soon as you remember it and space out the rest of the day’s doses evenly. If it is almost time for the next dose, do not double up the dose.

Overdose

Acyclovir overdose can result in agitation, confusion, sleepiness, lethargy, hallucination, dizziness/drowsiness, loss of consciousness, tremors and even seizures in some cases. It may cause kidney problems such as a change in the amount of urine and unusual back/side pain.

If you or a loved one overdose on acyclovir, contact poison control immediately. There are two ways to contact poison control: go online to www.poison.org or call 1-800-222-1222. Both options are free to the public, confidential, and available 24 hours a day.

Can it be taken during pregnancy?

Aciclovir is safe to take during pregnancy. There have been no adverse effects reported in fetuses or newborns that have been linked to aciclovir use during pregnancy. 

Can it be taken during breastfeeding?

Aciclovir does transfer into breast milk but it is deemed safe during breastfeeding. There have been no adverse effects to the baby in reported cases and the American Academy of Pediatrics considers aciclovir to be safe while breastfeeding.

Medically Reviewed
Priyank Pandey
Written by Priyank Pandey on February 25, 2022Medically Reviewed by Kelly Johnson-Arbor, MD, Param Patel

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