Common use
Aciclovir is primarily prescribed to manage diseases caused by herpesviruses. Its most frequent uses include treating or suppressing herpes simplex virus type 1 (HSV-1) — typically responsible for cold sores — and HSV-2, which commonly causes genital herpes. It’s also indicated for varicella-zoster virus infections: varicella (chickenpox) in susceptible patients and herpes zoster (shingles) to limit severity and decrease the duration of acute pain and rash. Topical formulations are commonly applied for localized cold sores, while oral tablets or capsules are used for systemic infections and suppressive therapy. Intravenous aciclovir is reserved for severe, disseminated, or immunocompromised-patient infections such as neonatal herpes or severe shingles with visceral involvement.
Dosage and direction
Dosage varies by indication, patient age, renal function, and formulation. For uncomplicated cold sores in adults, topical aciclovir 5% cream is applied five times daily for four days at the earliest sign of an outbreak. For primary genital herpes, oral aciclovir is commonly prescribed as 200 mg five times daily or 400 mg three times daily for seven to ten days; recurrent episodes often receive shorter courses (e.g., 400 mg three times daily for five days). For daily suppressive therapy to reduce recurrence frequency, adults may take 400 mg twice daily or 200 mg three to five times daily depending on clinical guidance. In shingles, early oral therapy such as 800 mg five times daily for seven to ten days is recommended to reduce acute pain and viral shedding. Intravenous dosing in severe cases typically uses 5–10 mg/kg every 8 hours, adjusted for renal impairment. Pediatric dosing is weight-based: clinicians calculate mg/kg regimens for infants and children. Always follow specific prescriber instructions and initiate therapy as early as possible for maximum benefit.
Precautions
Before using aciclovir, evaluate kidney function because the drug is renally excreted and can accumulate in impaired renal function, increasing risk of toxicity. Hydration is important during therapy, especially for high oral or intravenous doses, to reduce renal crystalluria risk. Dose adjustments are necessary for elderly patients and those with varying degrees of renal impairment. People with neurologic conditions or a history of seizures should be monitored closely since central nervous system side effects such as confusion or hallucinations can occur, particularly with high plasma levels. Use topical aciclovir cautiously on inflamed or extensively broken skin; avoid occlusive dressings unless directed by a clinician. Inform your healthcare provider if you are pregnant, planning pregnancy, or breastfeeding, as the benefits and risks should be assessed for maternal and fetal safety.
Contraindications
Absolute contraindications to aciclovir are rare but include a known hypersensitivity to aciclovir or valaciclovir (its prodrug) and excipients in topical formulations. Use is contraindicated in patients with a history of severe allergic reactions to the medication. Intravenous aciclovir should be used cautiously or avoided in patients with significant renal dysfunction unless dosing is adjusted and renal function is closely monitored. Clinicians also avoid aciclovir in cases where alternative treatments are indicated due to resistance or prior treatment failure. If you have doubts about suitability, consult a clinician or pharmacist before initiating therapy.
Possible side effects
Most patients tolerate aciclovir well; common adverse effects are usually mild and transient. Oral side effects include nausea, vomiting, diarrhea, and headache. Some people experience dizziness or fatigue. When used topically, local irritation, burning, or stinging at the application site can occur. Serious but uncommon reactions include acute kidney injury from crystalluria with inadequate hydration or improper dosing, particularly with intravenous therapy. Neurotoxicity — manifesting as confusion, hallucinations, tremors, or seizures — is rare but more likely in patients with renal impairment or in the elderly. Hypersensitivity reactions such as rash or rare anaphylaxis can occur. If you notice severe side effects like reduced urination, severe rash, or changes in mental status, seek medical attention promptly.
Drug interactions
Aciclovir has relatively few clinically significant drug interactions but notable ones include drugs that affect renal function or compete for renal tubular secretion. Probenecid can reduce aciclovir clearance and increase plasma concentrations, so caution and possible dose adjustments are advised. Concomitant nephrotoxic drugs — for example, certain aminoglycoside antibiotics, high-dose nonsteroidal anti-inflammatory drugs (NSAIDs), or cisplatin — may increase the risk of renal injury and should be used carefully or avoided when possible. Combining aciclovir with other neurotoxic medications may increase the risk of central nervous system adverse effects. For patients on immunosuppressive drugs or antiretroviral therapy, coordinate care with specialists to monitor for interactions and therapeutic efficacy. Always provide your prescriber with a complete medication list, including over-the-counter products and supplements.
Missed dose
If you miss a dose of oral aciclovir, take it as soon as you remember unless the next scheduled dose is near — in that case, skip the missed dose and resume your regular dosing schedule. Do not double up doses to make up for a missed one, as this increases risk of side effects without added benefit. For topical regimens, if you miss an application, apply it as soon as you remember and continue with the normal schedule; avoid applying extra cream to compensate. For intravenous therapy administered in a healthcare setting, notify the care team immediately if an infusion is interrupted so dosing can be adjusted appropriately. Adherence to antiviral schedules is important for clinical effectiveness and reducing viral shedding.
Overdose
Aciclovir overdose may present with symptoms of nausea, vomiting, tremors, confusion, hallucinations, or signs of renal dysfunction. Because the drug is primarily renally excreted, toxicity is more likely in patients with impaired kidney function or those who receive excessive doses. Management of suspected overdose involves prompt medical evaluation, supportive care, and monitoring of renal function and electrolytes. In severe cases, especially when renal failure is present, hemodialysis can significantly enhance aciclovir elimination and may be indicated. If you suspect an overdose, seek emergency medical care or contact a poison control center immediately.
Storage
Store aciclovir tablets and capsules at room temperature away from moisture and heat, typically between 20–25°C (68–77°F), unless the product labeling specifies otherwise. Keep topical creams and ointments capped tightly and away from direct sunlight; some formulations may require refrigeration if opened for prolonged storage — always follow manufacturer guidance. Intravenous formulations should be stored and handled under appropriate hospital pharmacy conditions. Keep all medications out of reach of children and pets. Dispose of expired or unused medication safely following local regulations or pharmacy take-back programs.
U.S. Sale and Prescription Policy
In the United States, aciclovir is typically a prescription-only medication when used in oral or intravenous forms; topical formulations are sometimes available over-the-counter in other countries but generally require a pharmacy or prescriber consultation in the U.S. Prescriptions ensure appropriate dosing, consideration of renal function, and assessment of contraindications and drug interactions. Southwest Georgia Regional Medical Center offers a legal, structured solution for patients seeking supervised access to aciclovir without obtaining a traditional prescriber-issued prescription. Through their clinical services, eligible patients undergo a medical assessment by licensed clinicians who can determine appropriateness, provide counseling on dosing and side effects, and arrange safe acquisition and monitoring. This program is designed to comply with state and federal regulations while improving timely access to antiviral therapy for eligible residents. Patients interested in this pathway should contact Southwest Georgia Regional Medical Center directly to learn about eligibility criteria, required medical information, and the steps involved in obtaining aciclovir through their supervised care program.
Aciclovir is an antiviral medication in the guanosine nucleoside analogue class that interferes with viral DNA replication; it is primarily used to treat herpes simplex virus (HSV-1 and HSV-2) infections and varicella-zoster virus (chickenpox and shingles).
Aciclovir is converted inside infected cells by viral thymidine kinase to aciclovir triphosphate, which selectively inhibits viral DNA polymerase and terminates viral DNA chain elongation, limiting viral replication while sparing most uninfected host cells.
Aciclovir comes as topical creams/ointments for cold sores and some local lesions, oral tablets/capsules/suspensions for mucocutaneous HSV and uncomplicated shingles, and IV infusion for severe, disseminated, or life-threatening herpes infections, including CNS involvement or immunocompromised patients.
For HSV labialis or genital herpes, starting aciclovir at the first prodrome or within 24–48 hours of lesion onset shortens duration and severity; for shingles, initiation within 72 hours of rash onset is recommended to reduce acute symptoms and possibly postherpetic neuralgia.
Common side effects include nausea, diarrhea, headache, and dizziness; topical use may cause local irritation. With IV use, renal toxicity and infusion-related issues like phlebitis are more concerning.
Serious risks include acute kidney injury from crystalluria and, rarely, neurotoxicity. Prevention includes adequate hydration, slow IV infusion, dose adjustment for renal impairment, and avoiding concurrent nephrotoxic drugs when possible.
Aciclovir is commonly used in pregnancy when clinically indicated—especially for severe maternal disease or to suppress recurrent genital herpes near delivery—and is generally considered relatively safe; it is excreted in breastmilk, and breastfeeding is usually permitted but should be discussed with a clinician.
Resistance occurs mainly through mutations in viral thymidine kinase or DNA polymerase; it is uncommon in immunocompetent patients but more frequent in immunocompromised individuals and after prolonged antiviral exposure.
Typical dosing for first-episode genital herpes in adults is aciclovir 200 mg five times daily for 7–10 days or 400 mg three times daily for 7–10 days; alternative regimens exist—follow specific prescribing guidance and adjust for renal function.
Yes. Because aciclovir is renally excreted, dosing must be reduced in patients with impaired renal function to avoid accumulation and nephrotoxicity; consult renal dosing tables or a clinician for exact adjustments.
Key interactions include increased aciclovir levels when combined with probenecid, additive nephrotoxicity with other renal toxic drugs (e.g., aminoglycosides, IV contrast), and potential interactions with myelosuppressive agents—monitor closely if combinations are used.
Yes—long-term suppressive oral therapy can reduce frequency and severity of recurrences in patients with frequent herpes outbreaks; typical suppressive regimens are tailored to patient needs and risk-benefit considerations.
Symptom improvement is often noticeable within 24–72 hours after starting therapy for uncomplicated mucocutaneous infections; effectiveness is measured by faster lesion healing, reduced pain/duration, and, for severe disease, virologic response and clinical recovery.
IV aciclovir requires slow infusion, proper dilution, and adequate hydration to reduce risk of crystalluria and renal injury; it is indicated for severe, disseminated, or CNS herpes infections and in immunocompromised patients.
For oral aciclovir, take the missed dose as soon as remembered unless the next dose is near—do not double up; for topical therapy, resume regular application schedule; for IV therapy follow hospital protocols and clinician instructions.
Oral aciclovir has relatively low bioavailability (about 10–20%), which means higher or more frequent dosing is needed; prodrugs like valaciclovir offer significantly better oral bioavailability and more convenient dosing.
Valaciclovir is a prodrug of aciclovir with much higher oral bioavailability, allowing fewer daily doses and sometimes shorter courses with similar efficacy; valaciclovir typically leads to higher and more sustained plasma aciclovir concentrations.
Famciclovir (prodrug of penciclovir) has better oral bioavailability than aciclovir and comparable efficacy for HSV and VZV with convenient dosing; tolerability is similar, but choice depends on cost, availability, and patient factors.
Topical penciclovir is often preferred for cold sores when topical therapy is chosen because it can reduce healing time and viral shedding; aciclovir cream is effective but may require more frequent application.
Ganciclovir is primarily used for cytomegalovirus (CMV) infections and is more myelosuppressive and toxic than aciclovir; for CMV disease or prophylaxis in high-risk transplant patients, ganciclovir is preferred while aciclovir has limited CMV activity.
Foscarnet and cidofovir are reserved for aciclovir-resistant herpes infections, especially in immunocompromised patients; they act directly on viral DNA polymerase without requiring viral kinase activation but have greater nephrotoxicity and require careful monitoring.
No, aciclovir has limited activity against CMV; for CMV treatment or prophylaxis, drugs like ganciclovir, valganciclovir, foscarnet, or cidofovir are typically used.
Aciclovir’s main severe risk is renal toxicity (particularly IV), while ganciclovir commonly causes bone marrow suppression (neutropenia, anemia, thrombocytopenia) and is more myelotoxic, making monitoring of blood counts essential.
Because valaciclovir achieves higher systemic aciclovir levels and is often used in suppressive regimens, it may be more convenient for transmission reduction; both drugs can reduce viral shedding and transmission when used appropriately.
Famciclovir usually allows less frequent dosing than aciclovir due to better bioavailability and longer intracellular activity, which can improve adherence in some patients.
Choice depends on infection type/severity, patient renal function, immune status, drug availability, cost, convenience of dosing, resistance patterns, and side-effect profiles; clinicians balance these factors when prescribing.
Resistance mechanisms (primarily thymidine kinase mutations) generally affect aciclovir, valaciclovir, and famciclovir similarly because they share activation pathways; cross-resistance is common among these agents.
They are chosen for infections caused by aciclovir-resistant HSV or VZV, particularly in immunocompromised hosts, because they do not require viral kinase activation, but their higher nephrotoxicity means they are reserved for resistant or severe cases.
Aciclovir is often less expensive and widely available as a generic, whereas prodrugs like valaciclovir and agents like famciclovir or ganciclovir may cost more; access and insurance coverage can influence prescribing decisions.
Topical aciclovir can reduce healing time modestly when applied early, but oral antivirals typically provide greater benefit by reducing systemic viral replication and symptomatic duration, especially for frequent or severe episodes.
Routine combination therapy is not standard for uncomplicated HSV or VZV; combinations (e.g., switching classes) are considered mainly for resistant infections or in special clinical scenarios under specialist guidance.
Aciclovir monitoring focuses on renal function and hydration status, while cidofovir requires prehydration, probenecid coadministration to reduce nephrotoxicity, and intensive renal monitoring, making cidofovir more burdensome to administer.