Acyclovir Dosage Guide for Adults

TL;DR

• For genital herpes, standard adult dose is 200 mg five times daily for 10 days (first outbreak) or 200 mg five times daily for 5 days (recurrent outbreaks), and 400 mg twice daily for long-term suppression.

• For shingles, dose jumps to 800 mg five times daily for 7 to 10 days, and treatment should start within 48 hours of rash appearing for best results.

• Kidney function matters with acyclovir because drug is cleared through kidneys, so your doctor may lower dose if you have any renal impairment.

How Does Acyclovir Work?

Acyclovir is an antiviral medication that targets herpes family viruses. It does not kill virus outright. Instead, it blocks virus from copying its DNA, which slows down replication and gives your immune system a better chance to control outbreak.

It is FDA approved for genital herpes and herpes simplex encephalitis. Doctors also widely prescribe it for shingles (herpes zoster) and chickenpox (varicella), even though those uses are technically considered off-label. The NCBI StatPearls overview on acyclovir covers full scope of its approved and off-label applications.

One important thing to understand is that acyclovir works best when started early. For any condition it treats, beginning medication at first sign of symptoms leads to better outcomes.

What Is Dosage for Genital Herpes?

Genital herpes dosing depends on whether you are dealing with a first episode, a recurrent outbreak, or trying to prevent future flare-ups.

First episode: 200 mg taken orally every four hours, five times daily, for 10 days. This is a longer course because initial outbreak tends to be most severe. The virus is new to your body, so symptoms like painful blisters, flu-like aches, and swollen lymph nodes are often more intense. If you are experiencing your first outbreak, this guide on what to expect during a first herpes outbreak walks through typical timeline and symptoms.

Recurrent outbreaks: 200 mg every four hours, five times daily, for 5 days. Treatment should begin at very first sign of a recurrence, ideally during tingling or burning stage before blisters fully form. The earlier you start, shorter and milder outbreak tends to be.

Suppressive therapy: 400 mg twice daily, taken every day for up to 12 months. After a year, your doctor will reassess whether you still need daily suppression based on how frequently your outbreaks have been occurring. Some people stay on suppressive therapy for years if outbreaks are frequent.

What Is Dosage for Shingles?

Shingles requires a higher dose because varicella-zoster virus is harder to suppress than herpes simplex. The standard adult dose is 800 mg every four hours, five times daily, for 7 to 10 days.

Timing is critical with shingles. Treatment should ideally begin within 48 hours of rash appearing. Starting early reduces severity of rash, speeds healing, and lowers risk of postherpetic neuralgia, which is lingering nerve pain that can persist for months after rash heals.

If you are trying to figure out what stage your outbreak is in, this article on herpes photos in different stages can help you identify where things stand.

What Is Dosage for Chickenpox?

For adults and children over 40 kg (about 88 pounds), chickenpox dose is 800 mg four times daily for 5 days. Treatment should start within 24 hours of rash appearing. Adults tend to have more severe chickenpox than children, so early antiviral treatment is especially important in this group.

Does Kidney Function Affect Dose?

Yes, and this is one of most important things to know about acyclovir. The drug is almost entirely cleared through kidneys. If your kidneys are not functioning at full capacity, acyclovir can build up in your body and increase risk of side effects like confusion, tremors, or kidney injury.

Your doctor will check your kidney function before prescribing acyclovir and may reduce dose or extend time between doses if your creatinine clearance is low. Older adults are especially susceptible because kidney function naturally declines with age. Staying well hydrated while taking acyclovir also helps protect kidneys by keeping drug from crystallizing in renal tubules.

Common Side Effects

Most people tolerate acyclovir well. The most frequently reported side effects in clinical trials were nausea, diarrhea, headache, and malaise. These tend to be mild and do not usually require stopping medication. Taking acyclovir with food can help reduce stomach upset.

More serious side effects are rare but include kidney problems (especially with IV use or dehydration), confusion or hallucinations in elderly patients, and severe skin reactions. If you notice any unusual symptoms, contact your provider.

Conclusion

Acyclovir dosing varies by condition. Genital herpes uses lower doses (200 to 400 mg), shingles requires higher doses (800 mg five times daily), and chickenpox falls in between. Starting treatment early and staying hydrated are two most important things you can do to get best results. If you have any kidney concerns, make sure your doctor adjusts dose accordingly.