Zovirax (Acyclovir) Tablets: Uses, Dosage, and Safety Information

Zovirax is the brand name under which we offer oral acyclovir tablets, a well-established antiviral medicine used to treat and manage outbreaks caused by herpes simplex virus and varicella-zoster virus. We carry Zovirax in 200 mg, 400 mg, and 800 mg tablets, so customers can match the strength and package size to the regimen a prescriber has recommended. This article explains what acyclovir does, how it is generally dosed, what to watch for during treatment, and how it compares with related antiviral options such as valacyclovir.

What Is Zovirax (Acyclovir)?

Zovirax tablets contain acyclovir, a synthetic nucleoside analogue belonging to the antiviral drug class identified by the ATC code J05AB01. Acyclovir was one of the first antiviral agents developed specifically to target herpesviruses, and oral acyclovir remains a standard treatment option for several herpesvirus-related conditions today. Each Zovirax tablet is taken by mouth, and we offer it in three strengths, 200 mg, 400 mg, and 800 mg, which allows a treatment plan to use the exact tablet size a prescriber has specified rather than requiring a patient to split or combine other strengths.

Understanding Herpes Infections

Herpes simplex virus type 1 and type 2 cause cold sores and genital herpes, conditions marked by painful blisters or ulcers that can recur periodically after the initial infection, because the virus becomes dormant in nerve tissue between outbreaks. Varicella-zoster virus, a related herpesvirus, causes chickenpox on first infection and can reactivate later in life as shingles, a painful rash that follows a nerve pathway. Because these viruses persist in the body, treatment focuses on shortening outbreaks, reducing viral shedding, and, in some cases, preventing recurrences, rather than eliminating the virus entirely.

How Acyclovir Works

Acyclovir is a guanosine analogue that depends on a viral enzyme, thymidine kinase, for its initial activation. Herpes simplex and varicella-zoster viruses produce their own thymidine kinase, which converts acyclovir into acyclovir monophosphate far more efficiently inside infected cells than host-cell enzymes do in uninfected cells. Host cell enzymes then complete the conversion to acyclovir triphosphate, the active form. This triphosphate competes with the natural building block of viral DNA and, once incorporated into a growing DNA strand, terminates that strand, effectively halting viral DNA synthesis. Because this activation step relies heavily on a viral enzyme, acyclovir concentrates its antiviral action in infected cells, which underlies its favorable safety profile in uninfected tissue.

Evidence Behind Acyclovir Therapy

Oral acyclovir has been studied extensively since its introduction in the 1980s, with clinical trials establishing its role in shortening the duration of herpes zoster rash, reducing pain associated with shingles, shortening genital herpes episodes, and lowering the frequency of recurrences when used as suppressive therapy. Studies in immunocompetent adults have shown that starting acyclovir within 72 hours of a herpes zoster rash appearing reduces the duration of viral shedding and accelerates lesion healing, while decades of use in genital herpes have confirmed that early treatment shortens symptomatic episodes by roughly one to two days on average. Long-term suppressive regimens have demonstrated meaningful reductions in outbreak frequency for people with recurrent genital herpes, an effect documented across multiple controlled trials referenced in acyclovir's prescribing history.

Formulation and Ingredients

Zovirax tablets are formulated for oral administration and are built around a single active ingredient, acyclovir, at the labeled strength on each tablet. Tablets also contain standard pharmaceutical excipients that support tablet formation, stability, and disintegration; these do not carry independent antiviral activity but affect how the tablet behaves after swallowing. Acyclovir tablets can generally be taken with or without food, since food has only a modest effect on how much acyclovir the body absorbs, though drinking plenty of water alongside each dose supports normal kidney handling of the medicine.

Established Uses of Oral Acyclovir

Oral acyclovir is established for treating herpes zoster (shingles), for treating initial and recurrent episodes of genital herpes, for long-term suppressive therapy in people with frequent genital herpes recurrences, and for treating chickenpox in adults and in children aged 2 years and older, using weight-based dosing in the pediatric population. Safety and effectiveness in children younger than 2 years have not been established. Some prescribers also use acyclovir off-label for other herpesvirus-related presentations, based on clinical judgment. We stock the tablet strengths most commonly prescribed across these situations, letting a prescription specify the strength and course length that fits the diagnosis.

Available Strengths, Packaging, and General Dosing Principles

We currently offer Zovirax acyclovir tablets in 200 mg, 400 mg, and 800 mg strengths. The 200 mg strength is available in packages of 180 or 360 pills, the 400 mg strength in packages of 60, 90, 120, 180, 270, or 360 pills, and the 800 mg strength in packages of 30, 60, 90, 120, 180, 270, or 360 pills, giving customers flexibility to order a supply that matches a short course or a longer suppressive regimen. General dosing patterns established for acyclovir vary considerably by condition: genital herpes episodes are commonly treated with 400 mg taken three times daily for seven to ten days, or 200 mg five times daily, while recurrent episodes often use shorter five-day courses at similar or higher per-dose amounts. Herpes zoster typically calls for a higher total daily dose, often 800 mg taken five times daily for seven to ten days, reflecting the higher acyclovir exposure needed against varicella-zoster virus. Suppressive therapy for recurrent genital herpes generally uses a lower, steady dose such as 400 mg twice daily over an extended period. These figures describe how acyclovir is generally used in practice; an individual regimen, including strength, frequency, and course length, should always follow a prescriber's specific instructions rather than being selected independently.

Elimination and Half-Life

Absorbed acyclovir is eliminated primarily by the kidneys, through a combination of glomerular filtration and active tubular secretion, with the majority of an absorbed dose recovered unchanged in urine. In people with normal kidney function, acyclovir's elimination half-life is approximately 2.5 to 3.3 hours, meaning blood levels fall substantially within several hours of each dose, which is part of why oral regimens typically require multiple daily doses rather than once-daily dosing. Reduced kidney function slows this clearance meaningfully, extending the half-life and requiring dose or frequency adjustments that a prescriber determines based on renal status. Oral bioavailability of acyclovir is limited, roughly 10 to 20 percent, and tends to decrease further at higher single doses, a pharmacological limitation that later led to the development of prodrug alternatives with improved absorption.

Important Safety Information

Most people tolerate oral acyclovir well, but a few groups warrant particular care. Pregnant patients should use acyclovir only when a clinician judges that the potential benefit justifies the potential risk, since acyclovir crosses the placenta. Acyclovir is excreted into breast milk, so caution is advised when it is used by a nursing parent. Older adults and anyone with reduced kidney function may need dose adjustments, because slower elimination can raise drug levels. Because dizziness and other nervous system effects have been reported, some patients should avoid driving or operating machinery until they know how the medicine affects them.

Reviewing known allergies, current medical conditions, other medicines being taken, pregnancy or breastfeeding status, and confirming that the tablet form matches what has been prescribed all help ensure that a course of Zovirax fits an individual health situation safely from the first dose.

Prescription Requirements and Ordering With Us

In the United States, acyclovir is authorized for human medicinal use, and the oral tablet form is classified as a prescription medicine. That means a prescriber's authorization is generally required to obtain this medicine legally, separate from any store-specific process. When customers order Zovirax through our catalog, our pharmacist-supported team is available around the clock by online chat, email, or phone to answer questions about the ordering process and help make sure the strength and quantity selected match what has been prescribed. If a question arises about a specific order, our support team can walk through the details directly rather than leaving customers to guess at the requirements.

Who Should Avoid Acyclovir

Acyclovir tablets are contraindicated for anyone with a known hypersensitivity to acyclovir or to valacyclovir, the prodrug that the body converts into acyclovir. Beyond this specific allergy history, there is no broad class of allergies that automatically rules out acyclovir use, but anyone with a history of a serious drug reaction should discuss it with a prescriber before starting treatment. People with significant kidney impairment are not excluded from acyclovir use outright, but they typically need adjusted dosing and closer monitoring rather than avoidance altogether.

Drug and Condition Interactions

Acyclovir has relatively few clinically significant drug interactions compared with many antivirals, but a handful are worth knowing. Probenecid and cimetidine can reduce the kidney's ability to clear acyclovir, raising blood levels and the chance of side effects. Combining acyclovir with other medicines that stress the kidneys, such as certain other nephrotoxic drugs, may increase the risk of kidney-related side effects, so kidney function is sometimes monitored more closely in that setting. Zidovudine, used in HIV treatment, has occasionally been associated with increased drowsiness when combined with acyclovir. Mycophenolate, an immunosuppressant, can also interact with acyclovir through shared renal elimination pathways. Anyone taking other prescription or over-the-counter medicines, including supplements, should share a complete list with their prescriber before starting Zovirax.

Side Effects and When to Seek Help

The most commonly reported side effects of oral acyclovir include headache, nausea, vomiting, diarrhea, and general malaise, most of which are mild and resolve on their own as treatment continues or ends. Some patients experience dizziness or fatigue. These ordinary effects usually do not require stopping treatment, though anyone bothered by persistent symptoms should mention them to a prescriber.

Less common but more serious reactions call for prompt attention. Signs of an allergic reaction, such as rash, hives, swelling of the face or throat, or difficulty breathing, require immediate medical care. Confusion, agitation, hallucinations, tremors, or unusual drowsiness, particularly in someone with reduced kidney function or in older adults, can indicate nervous system toxicity and should be reported to a healthcare provider right away. A noticeable drop in urine output, swelling, or other signs of kidney trouble also warrant urgent evaluation. Anyone experiencing a severe or rapidly worsening reaction should seek emergency medical attention without delay.

Overdose and Accidental Exposure

Taking substantially more acyclovir than prescribed, or accidental ingestion by someone the medicine was not prescribed for, can lead to kidney injury, since a large drug load can precipitate within the kidneys' filtering structures, along with nausea, vomiting, agitation, or seizures in more severe cases. Adequate hydration supports normal kidney clearance of the drug, and hemodialysis has been shown to effectively reduce blood acyclovir levels in overdose situations, since the drug is efficiently removed by dialysis. Anyone who suspects an overdose, whether their own or another person's, should contact emergency services or a poison control center immediately rather than waiting for symptoms to develop further.

Storage Instructions

Store Zovirax tablets at 59°F to 77°F, in a dry place, protected from light and moisture, consistent with standard storage principles for oral tablet medicines. Keeping the tablets in their original packaging until use, away from bathroom humidity and out of reach of children and pets, helps preserve their quality for the full course of treatment. Any tablets that are discolored, crumbling, or past their expiration date should not be used.

Benefits and Trade-Offs of Oral Acyclovir

Acyclovir's long track record, well-characterized safety profile, and relatively low cost make it a practical option for treating herpes simplex and varicella-zoster infections. Its main practical drawback is dosing frequency: because of its short half-life and limited oral absorption, effective regimens often require three to five doses a day, which can be harder to maintain consistently than once- or twice-daily alternatives. Valacyclovir, a prodrug that the body converts into acyclovir after absorption, achieves much higher bioavailability and allows less frequent dosing for comparable clinical effect, which is why some prescribers favor it for convenience. Famciclovir, a prodrug of penciclovir, offers a similar dosing advantage through a related mechanism that inhibits viral DNA polymerase. Topical antiviral options, such as penciclovir cream or docosanol cream, are sometimes used for localized cold sore treatment but do not reach the systemic drug levels needed for genital herpes, shingles, or chickenpox. Choosing among these options generally comes down to the specific herpesvirus condition being treated, dosing convenience, and a prescriber's clinical judgment for the individual case.

Generic Acyclovir and Other Antiviral Options

Zovirax is one branded presentation of the active ingredient acyclovir, and customers who are specifically looking for the generic form can find it listed separately as acyclovir in our catalog, alongside Zovirax itself. For those whose prescriber has specified a prodrug alternative instead, we also carry Valtrex, the valacyclovir-based option that offers similar antiviral coverage with a different dosing schedule. Customers exploring other antiviral treatments for herpes-related conditions are welcome to browse our broader AntiVirals selection to compare available forms and strengths. Whichever option fits a particular treatment plan, our team remains available to help match the exact product, strength, and package size to what has been prescribed.