Aclovir

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Medically reviewed

Marina Burgos

Last updated on 10/01/2026

This page provides general, reference-level information compiled from official medical sources. It is not a substitute for professional medical advice, diagnosis, or treatment. For decisions about your health, please consult a qualified healthcare professional.

Overview of Aclovir

What is Aclovir?

Aclovir is an antiviral medication primarily used to manage infections caused by certain types of viruses. It belongs to a class of drugs known as synthetic purine nucleoside analogues. These medications work by interfering with the replication process of the virus, effectively slowing its spread within the body and allowing the immune system to better manage the infection.

Primary Uses

Aclovir is most commonly utilized in the treatment of various conditions associated with the herpes simplex virus (HSV) and the varicella-zoster virus (VZV). This includes the management of:

  • Cold sores: Recurrent outbreaks of herpes labialis.
  • Genital herpes: Treatment of initial and recurrent episodes of genital infections.
  • Chickenpox: Reduction of severity and duration of the varicella virus in children and adults.
  • Shingles: Management of herpes zoster, helping to reduce the intensity of the localized rash and associated discomfort.

Mechanism of Action

The medication is designed to be highly selective. Once it enters a virus-infected cell, it undergoes a chemical conversion that allows it to inhibit the viral DNA polymerase. By mimicking a component of viral DNA, it incorporates itself into the growing DNA chain and prevents further synthesis. This targeted approach focuses on cells currently replicating the virus, while having minimal impact on healthy, non-infected human cells.

Therapeutic Goals

While Aclovir is effective at treating active symptoms and suppressing viral activity, it is important to note that it is not a cure for viral infections. These viruses can remain dormant in the body even after symptoms resolve. The primary goals of treatment with Aclovir are to:

  • Decrease the duration of viral shedding.
  • Shorten the time it takes for lesions and sores to heal.
  • Reduce the severity of pain and physical symptoms during an outbreak.
  • Lower the frequency of recurrent episodes in patients with chronic viral activity.

Regulatory References

  1. Aciclovir (Acyclovir) on WHO Essential Medicines List
  2. Acyclovir Drug Information (MedlinePlus)

What side effects are possible with Aclovir?

Possible Side Effects and Safety Information

Adverse reactions associated with Aclovir, the brand name for acyclovir, are documented across multiple body systems, as reported in regulatory documents. These reactions are typically categorized by frequency of occurrence.

Commonly Reported Adverse Reactions

System-Organ Class Examples
Gastrointestinal Nausea, vomiting, diarrhea, abdominal pain
Nervous System Headache, dizziness
General Fatigue or malaise

Serious and Clinically Significant Adverse Reactions

Serious adverse reactions, while less common, are significant safety considerations, particularly with intravenous and high-dose oral administration. These include:

  • Renal Toxicity: Acute renal failure and kidney injury have been reported, primarily due to drug precipitation in the renal tubules, especially in cases of dehydration or rapid intravenous infusion. Monitoring of renal function and adequate hydration is a critical safety measure.
  • Neurotoxicity: Central nervous system effects such as confusion, agitation, hallucinations, seizures, and in rare cases, coma, have occurred. Elderly patients and those with pre-existing neurological or kidney impairment may be at increased risk.
  • Hypersensitivity: Severe allergic reactions, including anaphylaxis and angioedema (swelling of the face, tongue, or throat), have been documented.
  • Hematologic Syndromes: Thrombotic Thrombocytopenic Purpura/Hemolytic Uremic Syndrome (TTP/HUS), which involves blood clotting and red blood cell damage, has been reported in severely immunocompromised individuals.

Population-Specific Safety Notes

Regulatory warnings advise particular caution in certain populations. Due to potential accumulation and increased risk of central nervous system effects, elderly patients may require dosage adjustment. Patients with underlying kidney impairment also require dose modification and close monitoring. Aclovir is classified as Pregnancy Category B by the FDA, indicating that use during pregnancy is considered only when the potential benefits outweigh the possible risks to the fetus.

Overdose and Emergency Response

Overdose and When to Seek Help

Overdosage with Aciclovir (Aclovir) is primarily associated with documented effects on the central nervous system (CNS) and the renal system. The regulatory documents list specific clinical manifestations and required emergency actions.

Documented Overdose Manifestations

Symptoms reported following overdosage include confusion, agitation, hallucinations, tremor, somnolence, headache, and dizziness. Gastrointestinal effects such as nausea, vomiting, diarrhea, and abdominal pain have also been documented. Severe outcomes include Acute Renal Failure and serious CNS events like convulsions (seizures), encephalopathy, and coma.

Overdosage of the intravenous form is specifically linked to the risk of Aciclovir crystal precipitation in the renal tubules, which can lead to kidney compromise, indicated by elevated serum creatinine and blood urea nitrogen (BUN) levels.

When to Seek Immediate Medical Attention

Immediate medical attention is required for any suspected overdose. Emergency medical services must be contacted immediately if the affected person shows signs of collapse, has a seizure, or cannot be awakened.

There is no specific antidote known. Management is primarily symptomatic and supportive treatment. The official management procedures documented in regulatory labeling include the use of Haemodialysis (Hemodialysis) as it significantly enhances the removal of the substance from the blood.

Elderly patients and individuals with impaired renal function are noted in official labeling as being more susceptible to severe neurological and renal overdose outcomes and require close monitoring.

Therapeutic Uses of Aclovir

What Aclovir Treats: Main Uses and Benefits


Aclovir is commonly used across conditions presenting with acute episodes caused by the Herpes Simplex Virus (HSV) and Varicella-Zoster Virus (VZV). The medication is applied in addressing situations involving certain distressing symptoms such as the painful, blistering manifestations of cold sores, genital herpes, Shingles (Herpes Zoster), and Chickenpox. The medication helps address symptom clusters that include localized pain, burning, and itching, and is relevant when supportive symptom management is appropriate.

“Aclovir is relevant across domains where short-term symptom management is appropriate and contributes to improved comfort during periods of heightened symptoms.”

Aclovir contributes to easing the overall symptom load by helping relieve pain and discomfort and supporting the healing of sores. In high-risk scenarios, it is used in situations involving symptoms linked to organ-specific functional stress (like Herpetic Keratitis) and is applied in addressing conditions involving episodic or fluctuating manifestations in patients with frequent outbreaks or weakened immune systems. This usage may be part of a management plan intended to help patients cope more steadily with difficult episodes.

Quick Fact: Support for Localized Pain and Burning Symptoms

Regulatory References

  1. NIH MedlinePlus Drug Information

Eligibility and Restrictions for Use

The eligibility for using Aclovir (Aciclovir) is strictly governed by regulatory classifications that define permissible, restricted, and prohibited populations. This structure is centered on specific medical conditions and physiological statuses.

Contraindications and Absolute Non-Eligibility

Use is contraindicated in patients with a documented history of clinically significant hypersensitivity to the active substance, aciclovir, or to valaciclovir. Additionally, patients with certain rare hereditary metabolic disorders (e.g., Lapp lactase deficiency) must not use specific tablet formulations.

Restricted Use and Conditional Eligibility

The medicine is generally established for use in adults and adolescents. However, eligibility is constrained by organ function; both older adults and patients with impaired renal function require that dosage be formally adjusted due to the drug’s renal clearance. The label advises caution for patients with underlying neurological abnormalities or those at risk of dehydration, for whom adequate fluid intake must be ensured.

Age and Reproductive Status

For children under two years of age, eligibility for use depends on the specific indication, and treatment requires specific determination by a doctor. Use during pregnancy and lactation is conditional; official labels advise caution and recommend use only when the potential benefits outweigh the unknown risks.

What should I know about interactions with other medicines?

Aclovir’s interaction profile is documented in official government sources and is primarily defined by its elimination pathway and the risk of additive organ toxicity. Co-administration with certain medicinal products can lead to documented pharmacokinetic and pharmacodynamic interactions.

The most noted pharmacokinetic interaction involves Probenecid. Co-administration of Probenecid has been officially shown to reduce the active renal clearance and subsequent urinary excretion of Aclovir. This reduction directly causes an increase in the mean Aclovir half-life and the Area Under the Concentration-Time Curve (AUC), representing a clinically significant increase in systemic exposure.

A second domain involves pharmacodynamic interactions that require caution. Aclovir, when co-administered with potentially nephrotoxic agents, may increase the risk of renal dysfunction due to combined effects. Concurrently, co-administration with potentially neurotoxic agents may increase the risk of reversible central nervous system (CNS) symptoms. This interaction risk is specifically noted as being heightened in populations such as geriatric patients with underlying renal impairment due to altered baseline drug clearance.

The official prescribing information states that there is no effect of food on the absorption of Aclovir oral tablets. Therefore, administration is permitted with or without food. No other mandatory timing separation rules for co-administration are documented in the official labeling.

Mechanism of Action

Selective Activation by Viral Enzyme

Aclovir is an antiviral pro-drug that is converted into its active, inhibitory form only inside cells infected with the target virus. This required chemical modification, or phosphorylation, is catalyzed by the virus-specific enzyme thymidine kinase. This initial step is fundamental, as it restricts the drug's activation primarily to cells expressing the viral enzyme, providing mechanistic selectivity.


Termination of Viral DNA Chain

The activated drug acts as a competitive substrate, being accepted by the viral DNA polymerase and incorporated into the virus's developing DNA chain. This incorporation immediately terminates the chain because it lacks the necessary chemical structure for further elongation. The process also causes irreversible disabling of the viral DNA polymerase enzyme, inhibiting the viral nucleic acid replication cascade.


Suppression of Viral Proliferation

By blocking the virus's ability to produce functional new copies of its genetic material, this mechanism leads to the physiological outcome of suppressed viral multiplication. The resulting inhibition of DNA synthesis restricts the formation of new, functional virions, which in turn results in a reduction of replicating virus concentration.

Dosage and Administration Information

Aclovir (Aciclovir) is administered via multiple methods, including Oral (tablets, capsules, and suspension), Intravenous (IV) Infusion, Topical (cream), and Ophthalmic (ointment) routes. The specific regimen is determined by the intended use (acute treatment, prophylaxis, or suppression) and the patient's physiological status, with dosing based on clinical guidelines.

Official Administration Routes and Schedules

Oral forms of Aclovir may be taken with or without food and are recommended to be consumed with a full glass of water to support renal function.

Usage Pattern Standard Labeled Adult Dose Frequency and Duration
Acute Oral Treatment (e.g., HSV) 200 mg 5 times daily (e.g., every 4 hours, omitting nighttime) for 5 to 10 days
Suppressive Oral Therapy 400 mg Twice daily, typically for up to 12 months, followed by re-evaluation
Herpes Zoster (Shingles) 800 mg 5 times daily for 7 to 10 days

Administration Requirements and Adjustments

For systemic treatment, the Intravenous (IV) solution must be administered by slow infusion over at least one hour and must not be given by rapid bolus, intramuscular (IM), or subcutaneous (SC) injection. The solution requires dilution prior to infusion.

Dose adjustment is required for patients with impaired renal function (kidney function), with the frequency or dosage modified based on the measured creatinine clearance. Older adults may also require dose reduction due to likely age-related changes in renal function.

If an oral dose is missed, it should be taken as soon as it is remembered. However, if it is almost time for the next scheduled dose, the missed dose is skipped to maintain the regular schedule and prevent doubling the dose. Treatment initiation is typically most effective when started as early as possible after the onset of an episode.

Recent Clinical Evidence

Research Evidence / Overview of Studies for Aclovir


Evidence for Use in Treating Acute Herpes Simplex Virus (HSV) Infections

Research has been conducted across various short-term clinical trials and systematic reviews, applying both oral Aclovir and topical Aclovir (cream) to study outbreaks of cold sores (Herpes Labialis) and genital herpes. These studies were used in research exploring how symptoms change over time in immunocompetent adults and adolescents. Trials reported measurements of lesion healing time in the treated groups compared to control groups.

Measurements of lesion healing time that were generally smaller were reported in trials examining topical applications compared to those examining oral administration. Research provides insight into short-term changes in patient-reported experience during these episodes. Long-term outcomes are not well characterized, as most studies focus on the short duration of the acute episode itself.

Evidence for Use in Managing Acute Varicella-Zoster Virus (VZV) Infections

For conditions characterized by fluctuating or episodic manifestations like Shingles (Herpes Zoster) and Chickenpox (Varicella), researchers have conducted Randomized Controlled Trials (RCTs) and systematic reviews to study the use of oral Aclovir. These studies monitored outcomes related to acute or disruptive episodes, such as the time needed for the rash to fully crust. For Shingles, a key focus in research was exploring short-term symptom changes, specifically the duration and severity of the acute pain, and the incidence of persistent pain known as Postherpetic Neuralgia (PHN).

Studies reported measurements of rash healing time and acute pain duration in the observed groups compared to control groups. Findings were mixed and showed variability across studies regarding the measured incidence of long-term persistent pain (PHN). Evidence quality varies across studies, and the certainty remains low regarding the measured reduction of PHN compared to other similar antiviral medicines.

Evidence for Suppressive Therapy in Preventing Recurrences

The research to explore the impact of oral Aclovir on the frequency of recurrent outbreaks of genital herpes was evaluated in long-term RCTs and systematic reviews. Study populations included adults who experienced frequent recurrences of the condition. Data show patterns related to the frequency of recurrence measurements that were generally lower in the groups receiving continuous therapy compared to those receiving placebo. These findings describe group patterns, not personal outcomes.

However, the design of some of the older trials has been associated with certain limitations. Continuous research is needed to monitor for any changes in the viral sensitivity, particularly in patients who may have other complicating conditions.

What Scientific Research Indicates is Still Uncertain

The broader evidence landscape highlights areas where scientific knowledge remains incomplete or where findings are inconsistent. The evidence quality varies across studies, particularly for the full spectrum of outcomes related to chronic pain prevention following a Shingles outbreak. Comparative evidence with newer antiviral agents is sometimes lacking or limited to specific subgroups. Moreover, there is limited information for long-term outcomes, especially regarding the potential for viral resistance to develop with continuous use in certain key patient populations.

Key Studies & References

  1. Acyclovir Drug Information
  2. WHO Model List of Essential Medicines (Aciclovir entry for antiviral agents)

Frequently Asked Questions (FAQ)

Common questions about Aclovir (FAQ)


Q: Is Aclovir a treatment for the common cold or flu?

A: Aclovir is an antiviral medicine specifically developed to target and help control certain herpes viruses, such as Herpes simplex (HSV) and Varicella-zoster (VZV). According to official prescribing information, Aclovir is not indicated for treating the common cold, the flu, or any bacterial infections.


Q: Does Aclovir stop the virus completely or just slow it down?

A: Aclovir is designed to suppress viral multiplication. It does this by incorporating itself into the virus's developing DNA chain, which immediately stops the chain from growing further. This mechanism limits the virus's ability to create new copies of itself, reducing the concentration of the replicating virus in the body.


Q: How long does it usually take to feel a difference after starting Aclovir?

A: Official regulatory information indicates that for the majority of the conditions Aclovir treats, patients typically report starting to feel better after using the medicine for a few days. The time frame can vary depending on the specific infection being addressed and how early treatment was started.


Q: How long does Aclovir stay in my system?

A: The time it takes for Aclovir to be processed by the body is measured by its plasma elimination half-life. Official data reports this half-life generally falls between 2.5 and 3.3 hours.


Q: Are there any specific drinks or foods I should avoid while taking Aclovir?

A: Official prescribing information does not list any specific foods or non-alcoholic drinks that must be avoided while using Aclovir. However, the medicine is known to cause some central nervous system effects, such as dizziness. For this reason, caution is generally advised regarding alcohol consumption.


Q: Can Aclovir cause strange dreams or sleep problems?

A: Aclovir is documented to cause side effects that affect the nervous system, including reports of sleepiness, confusion, and hallucinations. These effects are noted particularly with high doses or in certain populations, like older adults. Unusual or strange dreams are not explicitly listed in the official side effect profiles.


Q: Are there any long-term effects of taking Aclovir for a long time?

A: Official research overviews state that scientific knowledge regarding the long-term outcomes for patients taking Aclovir is not fully characterized. Available information regarding these long-term effects remains limited in the current evidence base.


Q: What signs indicate an allergic reaction to Aclovir?

A: Signs of an allergic reaction documented in official regulatory sources include skin rash, hives, and itching. More severe reactions involve swelling of the face, tongue, lips, or throat, which is known as angioedema.


Q: Can Aclovir affect the results of blood tests?

A: Official regulatory sources list rare, serious adverse reactions that involve changes to blood components, such as low counts of certain white blood cells (leukopenia and neutropenia). Therefore, close blood monitoring is often part of the prescribed care, particularly when the medicine is given intravenously or in high doses.


Q: Is there a known interaction between Aclovir and alcohol?

A: Official drug interaction profiles do not list a formal, mandatory contraindication with alcohol. However, because Aclovir has the potential to cause side effects like dizziness and confusion that affect the central nervous system, caution is generally advised regarding alcohol consumption.


Q: Can I take pain relievers like ibuprofen or acetaminophen while on Aclovir?

A: Caution is noted in official safety information when Aclovir is taken alongside other medicines that may affect kidney function. This includes non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen. Co-administration with such drugs has been reported in safety signals as being associated with an increased risk of kidney injury.


Q: Does Aclovir interact with commonly used vitamins or supplements?

A: Official regulatory sources advise that there is insufficient data to determine if commonly used herbal remedies, vitamins, or supplements are safe to take with Aclovir. This is because these products are typically not tested for interaction effects in the same manner as prescription drugs.


Q: Is Aclovir safe to use if I have kidney problems?

A: Aclovir is eliminated from the body through the kidneys, so its use is restricted for patients who have impaired renal (kidney) function. Official requirements state that the dosage must be formally adjusted based on measured kidney function, and close monitoring of these patients is generally necessary.


Q: Can older adults (seniors) use Aclovir?

A: Older adults may require a dose reduction of Aclovir due to the natural, age-related changes that can occur in kidney function. Official safety information also notes that this population may have an increased risk of experiencing central nervous system side effects, such as dizziness or confusion.


Q: Are there specific warnings for people with liver conditions taking Aclovir?

A: While most warnings emphasize kidney function, Official regulatory information suggests that extra consideration is often applied when Aclovir is used by individuals with poor liver function. Rarely reported serious adverse reactions have included liver inflammation, known as hepatitis.


Q: Is Aclovir appropriate for use in children?

A: Aclovir is generally established for use in adolescents and adults. For children, official dosing requirements are conditional upon their age and the specific condition being treated. Regulatory information indicates that children two years and older may be given adult dosages, while for children younger than two, specific dose determination is necessary.


Q: Can Aclovir still work if I start taking it after the symptoms have been around for a few days?

A: Treatment with Aclovir is generally most effective when it is started as early as possible after the onset of an episode. Official labeling notes that clinical data is limited regarding the effects of treatment initiated after a specific time window, such as after 72 hours for herpes zoster or 24 hours for chickenpox.


Q: Why do doctors emphasize starting Aclovir early?

A: Official recommendations to start Aclovir early are based on the results of clinical trial data. These studies found that the medicine is most effective when treatment is initiated as soon as possible after the first signs of the condition appear.


Q: Are there any lifestyle changes recommended while taking Aclovir?

A: Official administration instructions emphasize the need for adequate hydration, as it is considered a critical safety measure when taking Aclovir. Ensuring this fluid intake is necessary to support kidney function and help reduce the risk of acute renal injury.


Q: Does taking Aclovir affect fertility?

A: Official data regarding reproductive health indicates that the available evidence does not show that Aclovir reduces fertility in either men or women.


Q: Is Aclovir known to interact with birth control pills?

A: Formal drug interaction screenings reported in regulatory-aligned information have not found a documented interaction between Aclovir and commonly used combination oral contraceptive pills.


Q: Does Aclovir have a high potential for drug dependence?

A: Aclovir is not classified by regulatory agencies as a controlled substance. Official prescribing information does not list the potential for drug dependence or abuse as a recognized risk associated with this medicine.


Q: Is it possible to become resistant to Aclovir over time?

A: According to official labeling, resistance to the drug can occur. Prolonged or repeated courses of Aclovir, particularly in severely immunocompromised individuals, have been reported to result in the selection of virus strains that have a reduced sensitivity to the medicine.


Q: Can I crush or split the Aclovir tablets?

A: Official administration instructions state that if an individual experiences difficulty swallowing the tablet, it may be dissolved in a small glass of water and stirred. If the tablet is dissolved, consuming the entire liquid amount is necessary to ensure the administration of the full prescribed dose.


Q: What should I know about taking Aclovir if I have a compromised immune system?

A: Official regulatory warnings indicate that caution is necessary when Aclovir is used by individuals who have pre-existing immune system problems. Severely immunocompromised patients have a reported risk of developing a rare, life-threatening blood disorder known as Thrombotic Thrombocytopenic Purpura/Hemolytic Uremic Syndrome (TTP/HUS).


Q: Is Aclovir considered a first-line treatment for its main uses?

A: Aclovir is recognized by major health authorities as a foundational medication. It is considered a standard course of therapy globally for managing the viral infections for which it is indicated.


Q: Is Aclovir excreted in breast milk?

A: Yes, official safety information indicates that the active ingredient in Aclovir passes into breast milk in very small amounts. Official regulatory documentation states that use during lactation is conditional, and should be considered only when the potential benefits are thought to outweigh the unknown risks to the infant.

How should Aclovir be stored and disposed of?

How to Store and Dispose of Aclovir

The storage and disposal requirements for Aclovir are strictly defined in official regulatory labeling to maintain the product's stability and ensure safety.


Storage Requirements

Aclovir oral forms must be stored at Controlled Room Temperature, typically 20 C to 25 C (68 F to 77 F). The medicine must be protected from light and moisture and kept in a tightly closed, light-resistant container. The oral suspension formulation is specifically restricted and must not be refrigerated or frozen. All forms must be stored out of the sight and reach of children.


Disposal Instructions

Expired or unused Aclovir must be disposed of according to local regulations. The product must not be thrown away via wastewater or household waste. Consult a pharmacist for guidance on proper disposal methods for unused or expired medicines.

Attention! Always consult to a doctor or pharmacist before using pills or medicines.

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