Acyclovir

Pronunciation: ay-SYE-kloh-veer.

Generic name: acyclovir (aciclovir)
Brand names: Zovirax (topical cream/ointment; US oral brand availability not independently verified in the sources reviewed for this page), APO-Aciclovir (Australia, TGA ARTG 159141, sponsor Arrotex Pharmaceuticals Pty Ltd), Aciclovir AN (Australia, TGA ARTG 182885)
Drug class: Synthetic nucleoside analogue antiviral (herpesvirus DNA polymerase inhibitor)
Form: Tablet, capsule, oral suspension, topical cream/ointment, intravenous injection
Route: Oral (tablet, capsule, suspension), intravenous, or topical (cream/ointment) depending on product and indication
Legal status: Prescription-only oral and injectable forms in the United States, United Kingdom, and Australia. This page does not cover topical cold-sore products or their supply status.

Supply Rules Vary

Trade names by country: United States · United Kingdom · Canada · Australia

Australia: Aciclovir AN (5) · Full directory

What acyclovir (aciclovir) is and how it works

Acyclovir is an antiviral medicine active against herpes simplex virus (HSV) and varicella-zoster virus (VZV). Oral acyclovir is used to treat or suppress genital herpes, chickenpox, and shingles (herpes zoster); intravenous acyclovir is used in hospital for more severe HSV/VZV disease. This page does not cover topical acyclovir cream, which is a separate product used for cold sores. (1) (2) (3) (4)

Acyclovir does not cure herpes infection and does not stop it being passed to another person. Starting treatment as soon as symptoms begin, and completing the full course, matters for effectiveness. People with reduced kidney function need dose adjustment.

Mechanism of action: how acyclovir (aciclovir) works

Acyclovir is a guanosine analogue that is selectively phosphorylated by herpesvirus-encoded thymidine kinase and then further phosphorylated by host cell kinases to the active triphosphate, which inhibits viral DNA polymerase and causes chain termination, giving it much greater activity against HSV/VZV-infected cells than uninfected cells. (2) (4)

What acyclovir (aciclovir) is used for

Genital herpes (first episode and recurrences, and long-term suppression)

Oral acyclovir treats initial and recurrent genital herpes episodes and can be used long-term (suppressive therapy, up to 12 months per current US labeling) to reduce how often outbreaks happen. The exact regimen and duration are indication- and country-label-specific. (2) (4)

Herpes zoster (shingles)

Oral acyclovir treats shingles in adults, generally started as early as possible after the rash appears. (2) (4)

Chickenpox (varicella)

Oral acyclovir treats chickenpox in adults and children over 2 years old, generally started within 24 hours of the rash appearing. (2) (1)

HSV and VZV in immunocompromised or severe disease (specialist/IV use)

Intravenous acyclovir is used in hospital for severe initial genital herpes in patients with normal immunity, for initial and recurrent mucosal/cutaneous HSV in immunocompromised patients, for herpes simplex encephalitis, for neonatal herpes infection, and for varicella-zoster (shingles) in immunocompromised patients. This page does not provide IV dosing; that decision and regimen belong to the treating hospital team. (3)

Before taking acyclovir (aciclovir)

Do not take / not appropriate for

Tell the prescriber before starting if you have had a serious allergic reaction to acyclovir, valacyclovir, or a product ingredient; the prescriber will decide whether acyclovir is suitable. (all products) (4)

Tell your clinician about

Kidney disease or reduced kidney function — the dose usually needs to be lowered.
Dehydration or difficulty drinking enough fluids.
A weakened immune system, HIV/AIDS, or a bone-marrow or organ transplant.
Pregnancy, plans for pregnancy, or breastfeeding.
Every other prescription medicine, non-prescription medicine, vitamin, and herbal product used, especially other medicines that affect the kidneys.

(1) (2) (4)

How to take acyclovir (aciclovir)

Take acyclovir exactly as prescribed, at evenly spaced times, usually several times a day depending on the indication.
Tablets, capsules, or suspension can generally be taken with or without food; follow the product leaflet.
Start treatment as soon as possible after symptoms begin, for the indications where early treatment is advised (shingles, chickenpox, first genital herpes episode).
Drink plenty of fluids throughout the day while taking acyclovir, especially at higher doses, because adequate hydration reduces the chance of a kidney problem.
Complete the full prescribed course even if you feel better, unless the prescriber tells you to stop.

(1) (4)

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5) (6)

Missed dose

Follow the product instructions for missed doses, or ask the prescriber or pharmacist. Do not take a double or extra dose to make up for a missed one.

Overdose

Contact a poison control center or emergency service immediately, or go to the nearest emergency room. Overdose has caused agitation, confusion, seizures, and reduced kidney function with less urine output; severe cases can lead to loss of consciousness. Hospital treatment, including hemodialysis in some cases of acute kidney injury, may be needed. (1) (2)

Side effects

Most people tolerate oral acyclovir well. Report new or worsening symptoms, especially reduced urination, confusion, or a rash, promptly.

Nausea, vomiting, or diarrhoea

What to notice: Stomach upset, loose stools, or loss of appetite.

What to do: Usually mild; tell the prescriber if it is severe or does not settle. (1) (2)

Headache, dizziness, or general tiredness (malaise)

What to notice: Mild headache or feeling unwell.

What to do: Tell the prescriber if severe, persistent, or accompanied by confusion. (2)

Reduced kidney function

What to notice: Little or no urination, swelling in the legs/ankles/feet, or unusual tiredness.

What to do: Contact the prescriber promptly; kidney problems, including cases requiring dialysis, have been reported, particularly with inadequate fluid intake or existing kidney disease. (2) (4)

Neurological symptoms

What to notice: Confusion, agitation, hallucinations, unsteadiness, or seizures.

What to do: Seek prompt medical attention; these effects are more common in older adults and people with reduced kidney function. (2)

Serious warnings

Kidney injury (including acute renal failure) — urgent

Symptoms: Markedly reduced urination, swelling, or unusual tiredness, especially at high doses or with inadequate fluid intake.

Action: Contact the prescriber urgently and maintain fluid intake as advised; the prescriber will decide whether the dose should be continued, adjusted, or paused. (2) (4)

Central nervous system reactions — urgent

Symptoms: Confusion, hallucinations, agitation, seizures, or coma, reported especially in older adults or people with reduced kidney function.

Action: Seek urgent medical assessment. These reactions are usually reversible when the dose is adjusted or the medicine is stopped under medical supervision. (2)

Severe allergic or skin reaction — emergency

Symptoms: Hives, facial or throat swelling, difficulty breathing, or a blistering/peeling skin rash.

Action: Seek emergency care immediately; a clinician or emergency service will decide whether Acyclovir needs to be stopped. (1) (2)

Blood-clotting disorder (thrombotic thrombocytopenic purpura / haemolytic uraemic syndrome) — urgent

Symptoms: Unusual bruising or bleeding, extreme tiredness, or yellowing of the skin or eyes; reported rarely, mainly in people with a severely weakened immune system.

Action: Contact the clinical team urgently for assessment and blood tests. (2)

Interactions

Medicine or test	Effect	Action
Other medicines that can affect the kidneys (e.g. some other nephrotoxic drugs)	May increase the risk of kidney problems when combined with acyclovir, particularly at higher doses or with dehydration.	Tell the prescriber about every medicine used so kidney function can be monitored if needed; do not combine without medical advice. (4)
Probenecid and cimetidine	May increase acyclovir blood levels by reducing its elimination.	The prescriber will decide whether monitoring or a dose change is needed. (4)
Mycophenolate mofetil (used after organ transplant)	Levels of both medicines may increase when combined.	Transplant and infectious-disease teams should coordinate dosing and monitoring; do not adjust either medicine yourself. (4)

Pregnancy, breastfeeding, kidney/liver function, age

Pregnancy

Current evidence has not shown an increase in birth defects, but acyclovir should be used in pregnancy only when a clinician judges the benefit justifies the possible unknown risk. Discuss your specific situation with the prescriber. (4)

Breastfeeding

Acyclovir passes into breast milk at levels higher than in the blood. Discuss the benefits and risks with the prescriber before breastfeeding during treatment. (4)

Reduced kidney function or older age

Dose and dosing interval usually need to be adjusted for reduced kidney function, and older adults are more likely to have reduced kidney function. The prescriber must use the current local label rather than a standard dose. (4) (2)

Children

Oral acyclovir is used in children for specific indications such as chickenpox, generally from 2 years old, with weight-based dosing decided by the prescriber. (2) (4)

Monitoring

Before starting

Assess kidney function, hydration status, and immune status.
Review current medicines for other kidney-affecting drugs, probenecid, cimetidine, or mycophenolate.

During treatment

Watch for reduced urine output, confusion, or unusual bruising/bleeding, especially at higher doses or in older adults and people with reduced kidney function.
Ensure adequate fluid intake throughout treatment.
Kidney function monitoring may be advised for higher-risk patients, per the prescriber's judgement and current local label.

(4) (2)

Storage

Store tablets/capsules at room temperature in the original container, tightly closed, away from excess heat and moisture, and out of sight and reach of children. Ask a pharmacist about safe disposal of unused medicine; do not flush it.

Professional information

Clinician-facing context only. Use the current local product label for exact regimens, renal dose-adjustment tables, and paediatric weight-based dosing.

United States (oral tablet label)

Indication: Genital herpes, herpes zoster, chickenpox

Dose summary: Regimens differ by indication (e.g. 200 mg five times daily for initial genital herpes for 10 days; 800 mg five times daily for herpes zoster for 7–10 days; 800 mg four times daily for 5 days for chickenpox in those over 40 kg). No universal regimen is displayed here; confirm the exact current dose, frequency, and duration against the current label.

Renal context: Dose and/or dosing interval must be adjusted for reduced creatinine clearance; maintain adequate hydration, particularly with IV or high-dose oral therapy. (2) (4)

Mechanism of action

Hepatic guidance

The reviewed US and UK product information does not give specific hepatic-impairment dosing guidance; renal function is the factor with an explicit, detailed dose-adjustment table. Discuss liver disease with the prescriber and use the current local label.

Overdose note

Overdose management is supportive; hemodialysis significantly enhances acyclovir removal and may be considered in acute renal failure. (2) (4)

Frequently asked questions

Does acyclovir cure herpes?

No. Acyclovir treats outbreaks and can reduce how often they happen, but it does not cure the underlying herpes infection and does not eliminate the risk of passing it to a partner. (1)

Why do I need to drink extra fluids while taking acyclovir?

Adequate hydration reduces the risk of a kidney problem, which is a recognised effect of acyclovir, particularly at higher doses. (4) (1)

Is oral acyclovir the same as the cream for cold sores?

No. Oral/systemic acyclovir and topical acyclovir cream are different products for different situations and are not interchangeable. This page covers oral/systemic use. (1)

What is the mechanism of action of acyclovir (aciclovir)?

What is the generic name of Acyclovir?

The generic name is acyclovir (aciclovir). It is sold under brand names including Zovirax (topical cream/ointment; US oral brand availability not independently verified in the sources reviewed for this page), APO-Aciclovir (Australia, TGA ARTG 159141, sponsor Arrotex Pharmaceuticals Pty Ltd), Aciclovir AN (Australia, TGA ARTG 182885). (1) (2) (3) (4) (5) (6)

What class of drug is acyclovir (aciclovir)?

Acyclovir is classed as: Synthetic nucleoside analogue antiviral (herpesvirus DNA polymerase inhibitor). (1) (2) (3) (4) (5) (6)

References

Acyclovir: MedlinePlus Drug InformationMedlinePlus, U.S. National Library of Medicine · United States · accessed 2026-07-26 · source 1
Acyclovir tablet — prescribing information (label updated 2026-02-27)U.S. National Library of Medicine DailyMed / FDA-sourced label · United States · accessed 2026-07-26 · source 2
Acyclovir Sodium injection, solution — prescribing informationDailyMed, U.S. National Library of Medicine · United States · accessed 2026-07-26 · source 3
Aciclovir 400 mg Tablets — Summary of Product Characteristics (Wockhardt UK Ltd)electronic Medicines Compendium (UK) · United Kingdom · accessed 2026-07-23 · source 4
ACICLOVIR AN aciclovir 400mg tablet blister pack — ARTG 182885Therapeutic Goods Administration · Australia · accessed 2026-07-26 · source 5
APO-ACICLOVIR aciclovir 800mg tablet blister pack — ARTG entry 159141Therapeutic Goods Administration (TGA), Australia · Australia · accessed 2026-07-26 · source 6

Brand names by country

Single-ingredient acyclovir (aciclovir) names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries

United States

Zovirax50 mg/g · bausch health us, llc
Avaclyr30 mg/g · fera pharmaceuticals, llc

United Kingdom

Aciclovir Tablets (Wockhardt UK Ltd) (4)current licensed product · 200 mg, 400 mg · Wockhardt UK Ltd, Wrexham, United Kingdom

Canada

ZOVIRAX

Australia

Aciclovir AN (5)current register product lower confidence source · 400 mg · Arrotex Pharmaceuticals Pty Ltd · Source verification is search-result-confirmed, not a live-opened TGA page (direct fetch timed out twice); re-verify with a live fetch before publication.

View brands in additional countries.