Acyclovir Dosage Guide: How Much to Take and When (With Chart)
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Acyclovir Dosage Guide: How Much to Take and When (With Chart)
Medically reviewed by Alan Lucks | MD , Alan Lucks MDPC Private Practice - New York on January 6th, 2026. Updated on June 25th, 2026
Key Takeaways
Acyclovir is an antiviral medication used primarily to treat herpes infections, including genital herpes, cold sores, and shingles.
Dosage varies widely depending on the condition being treated, the patient's age, and kidney function.
Typical adult doses range from 200 mg to 800 mg taken multiple times daily, with adjustments for children and those with kidney impairment.
Following prescribed dosage schedules closely is crucial to maximize effectiveness and reduce the risk of resistance.
Doctronic.ai offers personalized guidance on acyclovir dosage and connects you with licensed doctors for telehealth consultations at any time.
Understanding Acyclovir Uses and Dosages
Acyclovir dosage for cold sores is 200 mg taken five times daily for 5 days, started at the first sign of symptoms. The right dose varies by condition: genital herpes, shingles, and chickenpox each follow different schedules. Age, kidney function, and immune status also affect dosing. This guide breaks down the correct acyclovir dosage for every major use case so you know exactly how much to take and when.
Acyclovir Dosage Chart
Acyclovir Dosage by Condition
Genital Herpes
For initial episodes in adults, acyclovir is typically prescribed at 400 mg orally three times a day for 7 to 10 days. Recurrences are often treated with 800 mg orally twice daily for 5 days. For chronic suppression, 400 mg twice daily may be recommended to reduce the frequency of outbreaks.
Cold Sores (Herpes Labialis)
For cold sores, a common approach is 200 mg five times daily for 5 days. Early treatment at the first sign of symptoms can reduce healing time and severity.
Shingles (Herpes Zoster)
Shingles treatment usually involves 800 mg orally, taken 5 times a day for 7 to 10 days. This higher dose helps control the more severe viral activity and nerve pain associated with shingles.
Chickenpox (Varicella)
In children, acyclovir is dosed at 20 mg/kg orally four times daily for 5 days, ideally started within 24 hours of rash onset to reduce symptoms and complications.
Acyclovir Dosage for Cold Sores: What You Need to Know
Cold sores are caused by herpes simplex virus type 1 (HSV-1), and acyclovir is one of the most commonly prescribed oral antivirals for treating them. Starting treatment early is the single most important factor in how well acyclovir works for cold sores.
The standard acyclovir dosage for cold sores in adults is 200 mg taken five times per day, spaced roughly every 4 hours while awake, for 5 days. Some providers prescribe 400 mg three times daily as an alternative schedule that is easier to follow and equally effective for many patients. The goal of either regimen is to reduce the duration of the outbreak and relieve pain and swelling faster than the virus would resolve on its own.
When to Start Treatment
Acyclovir works best when taken at the very first sign of a cold sore, such as tingling, itching, or burning around the lips, before a blister fully forms. Starting within this prodromal window gives the medication the best chance to limit viral replication. Delaying treatment by even 24 to 48 hours reduces how much benefit you get from the course.
Suppressive Therapy for Frequent Cold Sores
If you get cold sores frequently (six or more outbreaks per year), a doctor may recommend long-term suppressive therapy. A typical suppressive dose is 400 mg taken twice daily on an ongoing basis. This approach does not cure HSV-1, but it significantly lowers the number of outbreaks and may reduce the risk of passing the virus to others during asymptomatic shedding.
Cold Sores vs. Canker Sores
A common point of confusion is the difference between cold sores and canker sores. Cold sores appear on or around the outside of the lips and are caused by a virus, making acyclovir appropriate. Canker sores appear inside the mouth and are not viral, so acyclovir will not help. If you are unsure which type of sore you have, our AI doctor can help clarify before you start treatment.
Pediatric Dosing for Cold Sores
Acyclovir is generally used in children for chickenpox rather than cold sores, but a provider may prescribe it off-label for severe or recurrent HSV-1 in a child. Dosing is weight-based in that scenario, typically around 20 mg/kg per dose, and should always be directed by a pediatrician.
What is the Typical Acyclovir Dose for Adults?
Adults receive varying doses depending on the infection. For example, oral doses for herpes simplex infections range from 200 mg to 800 mg taken 3 to 5 times daily. Intravenous doses are reserved for severe infections or immunocompromised patients, typically 5 mg/kg every 8 hours.
It’s essential to take acyclovir exactly as prescribed, maintaining consistent intervals between doses to keep adequate drug levels in the bloodstream.
What is the Typical Acyclovir Dose for Children?
Children’s doses are generally weight-based, around 20 mg/kg per day, divided into 3 to 5 doses. For severe infections, intravenous administration may be necessary with close medical supervision.
What to Do If You Miss a Dose of Acyclovir?
If a dose is missed, take it as soon as remembered unless it is almost time for the next dose. Do not double up doses to catch up. Maintaining a regular dosing schedule is key to effective treatment.
How to Adjust Your Acyclovir Dose for Certain Medical Conditions
Kidney Impairment Adjustment
The kidneys primarily eliminate Acyclovir. Patients with reduced kidney function require dose adjustments to prevent toxicity. This may involve lowering the dose or extending the interval between doses. Your healthcare provider will determine the best regimen based on kidney function tests.
Immunocompromised Patients
Patients with weakened immune systems, such as those undergoing chemotherapy or with HIV, often need higher or more frequent dosing to control viral replication effectively. Close monitoring is necessary to balance efficacy and side effects.
Acyclovir Overdose and Warnings
Overdose symptoms can include nausea, vomiting, dizziness, confusion, and, in severe cases, kidney damage or seizures. If an overdose is suspected, seek emergency medical attention immediately.
Common side effects include headache, diarrhea, and fatigue. Severe allergic reactions are rare but require urgent care.
Tips for Taking Acyclovir Safely
Take with plenty of water to help prevent kidney problems.
Complete the full course even if symptoms improve early.
Store medication at room temperature away from moisture and heat.
Inform your doctor about all medications and supplements to avoid interactions.
Consult your healthcare provider before starting or stopping acyclovir.
Learn More About Acyclovir Dosage With Doctronic
Acyclovir dosing can feel complicated, and the stakes are real. Doctronic's AI doctor is available 24/7 to answer questions about dosing schedules, side effects, and interactions, backed by the latest clinical research. Doctronic also connects you with licensed physicians for telehealth video visits across all 50 states, so you can get affordable, convenient care for your antiviral treatment needs. Visit Doctronic.ai to get started.
Frequently Asked Questions
The standard dose is 200 mg taken five times per day for 5 days, or 400 mg three times daily as an alternative. Treatment works best when started at the first sign of tingling or itching, before a blister fully develops. Ask our AI doctor if you are unsure which schedule is right for you.
Most people see their cold sore heal 1 to 2 days faster with acyclovir compared to no treatment, especially when started early. Pain and swelling typically begin to improve within the first 2 days of the course. Complete the full 5-day course even if symptoms seem to improve sooner.
Yes, oral acyclovir tablets require a prescription in the United States. Topical acyclovir cream is also prescription-only in the US, though it is less effective than oral therapy for cold sores. Our licensed physicians can evaluate you via telehealth and prescribe acyclovir if it is appropriate for your situation.
Yes, this is called suppressive therapy. A typical suppressive dose is 400 mg twice daily on an ongoing basis for people with six or more outbreaks per year. A doctor will help you decide whether long-term suppression is appropriate based on your outbreak frequency and overall health.
Yes, the kidneys are the primary route of acyclovir elimination, so reduced kidney function requires dose or frequency adjustments to avoid toxicity. Your provider will base the adjustment on your creatinine clearance or estimated GFR. Never adjust your dose on your own without guidance from a healthcare provider.
The Bottom Line
Acyclovir remains a trusted antiviral for managing herpes and related viral infections. Correct dosing tailored to your condition and health status ensures the best outcomes and minimizes side effects. If you are unsure about how much acyclovir to take or need help adjusting your dose, expert guidance is just a click away with Doctronic.ai .
