Aciclovir is a nucleoside analogue antiviral medication specifically designed to inhibit the replication of herpes viruses. As a first-line treatment for infections caused by herpes simplex virus (HSV) types 1 and 2 and varicella-zoster virus (VZV), it remains a cornerstone of antiviral therapy. Its mechanism of action involves selective phosphorylation by viral thymidine kinase, leading to chain termination and effective suppression of viral DNA synthesis. Clinicians worldwide rely on aciclovir for its proven efficacy, favorable safety profile, and well-established pharmacokinetics in managing both initial and recurrent episodes of herpes infections.

Features

• Synthetic nucleoside analogue with selective antiviral activity
• Available in multiple formulations: oral tablets, topical cream, intravenous injection, and suspension
• Chemical name: 2-amino-1,9-dihydro-9-[(2-hydroxyethoxy)methyl]-6H-purin-6-one
• Molecular formula: C₈H₁₁N₅O₃
• Molecular weight: 225.21 g/mol
• White to off-white crystalline powder
• Water solubility: 1.3 mg/mL at 25°C
• Plasma protein binding: 9-33%
• Half-life: 2.5-3.3 hours in adults with normal renal function

Benefits

• Effectively reduces healing time for herpes lesions by inhibiting viral replication
• Decreases duration of viral shedding, reducing transmission risk
• Alleviates pain and discomfort associated with herpes outbreaks
• Prevents new lesion formation when initiated early in infection
• Reduces frequency and severity of recurrent episodes with suppressive therapy
• Minimizes risk of complications in immunocompromised patients

Common use

Aciclovir is primarily indicated for the treatment of herpes simplex virus infections, including genital herpes, herpes labialis (cold sores), and herpes keratitis. It is equally effective against varicella-zoster virus, making it suitable for treating chickenpox and herpes zoster (shingles). In immunocompromised patients, including those with HIV/AIDS or undergoing chemotherapy, aciclovir serves as both treatment and prophylaxis against herpes infections. Off-label uses include prevention of cytomegalovirus (CMV) infection in transplant recipients and management of Epstein-Barr virus infections in specific clinical scenarios.

Dosage and direction

Dosage varies significantly based on indication, patient age, renal function, and immune status. For genital herpes initial episodes: 200 mg orally five times daily for 10 days. Recurrent episodes: 200 mg five times daily for 5 days. Chronic suppression: 400 mg twice daily or 200 mg three times daily. Herpes zoster: 800 mg five times daily for 7-10 days. Chickenpox in immunocompetent patients: 20 mg/kg (max 800 mg) four times daily for 5 days. Intravenous dosing for severe infections: 5-10 mg/kg every 8 hours. Topical application: Apply sufficient quantity to cover lesions every 3 hours, 6 times daily for 7 days. Always complete the full course even if symptoms improve earlier.

Precautions

Renal function must be assessed before initiation, particularly for intravenous administration, as aciclovir is primarily eliminated renally. Maintain adequate hydration during treatment to prevent crystal nephropathy. Use with caution in elderly patients due to age-related decline in renal function. Monitor neurological status as neurotoxicity may occur, especially with high doses or rapid intravenous infusion. Pregnancy category B: use only if potential benefit justifies potential risk. Breastfeeding considerations: aciclovir concentrates in breast milk; weigh benefits against potential infant exposure. Topical formulation may cause local irritation; avoid ocular contact.

Contraindications

Hypersensitivity to aciclovir, valaciclovir, or any component of the formulation constitutes absolute contraindication. Severe renal impairment (creatinine clearance <10 mL/min) without appropriate dose adjustment contraindicates standard dosing. Intravenous administration is contraindicated in patients with history of serious hypersensitivity reactions to aciclovir. Concomitant use with other nephrotoxic drugs requires extreme caution and may represent relative contraindication depending on clinical circumstances.

Possible side effect

Common side effects (≥1%) include nausea (2-5%), vomiting (1.5-3%), diarrhea (2-4%), headache (1-2%), and dizziness (0.5-2%). Topical application may cause burning, stinging, or pruritus at application site. Less frequent adverse reactions include fatigue, skin rash, and transient elevation of liver enzymes. Rare but serious side effects include acute renal failure (particularly with IV administration), neurotoxicity (agitation, confusion, hallucinations, seizures), thrombotic thrombocytopenic purpura/hemolytic uremic syndrome, and anaphylaxis. Hematological abnormalities including leukopenia and thrombocytopenia may occur with prolonged therapy.

Drug interaction

Probenecid significantly increases aciclovir plasma concentrations by reducing renal clearance. Concomitant use with other nephrotoxic agents (aminoglycosides, cyclosporine, NSAIDs) may enhance nephrotoxic potential. Zidovudine may cause increased drowsiness and lethargy when combined with aciclovir. Immunosuppressants may have enhanced effects due to aciclovir’s effect on rapidly dividing cells. No clinically significant interactions with oral contraceptives have been documented. Monitoring of drug levels and renal function is recommended when used with interacting medications.

Missed dose

If a dose is missed, take it as soon as remembered unless it is almost time for the next scheduled dose. Do not double the dose to make up for a missed one. For multiple daily dosing regimens, maintaining consistent intervals between doses is important for maintaining therapeutic plasma concentrations. If multiple doses are missed, contact healthcare provider for guidance on resumption of therapy. The clinical significance of missed doses depends on whether treatment is for active infection or suppression.

Overdose

Aciclovir overdose may manifest as elevated creatinine, renal failure, neurological symptoms (agitation, confusion, seizures), and gastrointestinal distress. Management includes supportive care with maintenance of adequate hydration to promote drug excretion. Hemodialysis significantly enhances aciclovir removal (approximately 60% reduction in plasma concentrations during 6-hour dialysis). In cases of recent ingestion, gastric lavage may be considered. Neurological symptoms typically resolve with discontinuation of therapy and supportive measures. There is no specific antidote for aciclovir overdose.

Storage

Store at controlled room temperature (15-30°C or 59-86°F). Protect from moisture and light. Keep oral formulations in tightly closed containers. Do not freeze oral suspension. Intravenous solution should be stored at controlled room temperature; after reconstitution, use within 12 hours. Do not refrigerate reconstituted solution as precipitation may occur. Topical cream should not be stored above 30°C. Keep all medications out of reach of children and pets. Properly discard expired medication according to local regulations.

Disclaimer

This information is provided for educational purposes only and does not constitute medical advice. Individual patient responses to aciclovir may vary based on numerous factors including age, renal function, immune status, and concomitant medications. Always consult with a qualified healthcare professional before initiating or modifying any treatment regimen. Dosage adjustments may be necessary based on individual patient characteristics. The prescriber should be familiar with complete prescribing information before administering aciclovir.

Reviews

Clinical studies consistently demonstrate aciclovir’s efficacy across various herpes virus infections. In genital herpes treatment, aciclovir reduces healing time by 3-4 days and decreases viral shedding duration. For herpes zoster, early initiation within 72 hours of rash onset significantly reduces acute pain and postherpetic neuralgia risk. Meta-analyses confirm its effectiveness in preventing recurrent herpes episodes with suppressive therapy reducing recurrence frequency by 70-80%. Long-term safety data spanning decades support its favorable risk-benefit profile. Recent comparative studies show continued relevance despite newer antivirals, particularly for specific patient populations and cost-effectiveness considerations.