Comprehensive Guide to Acyclovir: Uses, Dosage, Side Effects, and More

What is Acyclovir?

Overview of Acyclovir

Generic Name: Acyclovir

Brand Name: Zovirax, generics

Drug Group: Antiviral

Commonly Used For

• Treat herpes simplex infections.
• Manage varicella-zoster (chickenpox, shingles).
• Prevent recurrent herpes outbreaks.

Key Characteristics

Form: Oral tablets (200 mg, 400 mg, 800 mg), topical cream (5%), IV injection (500 mg/vial), ophthalmic ointment (detailed in Dosage section).

Mechanism: Selectively inhibits viral DNA synthesis.

Approval: FDA-approved (1982 for Zovirax) and EMA-approved for herpes and VZV infections.

Indications and Uses of Acyclovir

Acyclovir is indicated for a broad spectrum of viral infections, leveraging its targeted antiviral action:

Herpes Simplex Virus (HSV) Infections:

Treats initial and recurrent genital herpes (HSV-2), reducing lesion duration and viral shedding, effective within 72 hours of onset.

Manages orolabial herpes (HSV-1), including cold sores, alleviating pain and accelerating healing, suitable for immunocompetent and immunocompromised patients.

Prevents recurrent HSV in immunocompromised individuals (e.g., HIV patients), with suppressive therapy reducing outbreak frequency by up to 80%.

Varicella-Zoster Virus (VZV) Infections:

Treats chickenpox in children and adults, shortening disease course and preventing complications like pneumonia, most effective if started within 24 hours of rash.

Manages herpes zoster (shingles) in adults, reducing postherpetic neuralgia risk and lesion severity, particularly in those over 50 years.

Immunocompromised Patients:

Prevents and treats HSV and VZV infections in patients with cancer, organ transplants, or AIDS, where viral reactivation is common, often requiring IV administration.

Encephalitis:

Treats herpes simplex encephalitis (HSE), a life-threatening condition, with IV Acyclovir as the standard of care, improving survival rates when initiated early.

Off-Label Uses:

Includes management of Bell’s palsy associated with HSV reactivation, treatment of neonatal herpes simplex with high-dose IV therapy, and prophylaxis in stem cell transplant recipients to prevent VZV reactivation, supported by clinical studies and guidelines.

Adjunctive therapy in Epstein-Barr virus (EBV)-related lymphoproliferative disorders, under specialist oversight.

Treatment of disseminated VZV in immunocompromised patients, enhancing systemic control.

Ophthalmic Use:

Treats herpes keratitis and conjunctivitis, reducing corneal scarring and vision loss, applied as an ointment 5 times daily.

Dosage of Acyclovir

Dosage for Adults

Genital Herpes (Initial Episode, Oral): 200 mg 5 times daily (every 4 hours while awake) for 10 days, or 400 mg 3 times daily for 7–10 days.

Genital Herpes (Recurrent, Oral): 200 mg 5 times daily or 400 mg 3 times daily for 5 days, starting at first sign of outbreak.

Genital Herpes (Suppressive, Oral): 400 mg twice daily, continued for up to 12 months, adjusted for recurrence risk.

Herpes Zoster (Shingles, Oral): 800 mg 5 times daily for 7–10 days, initiated within 72 hours of rash.

Chickenpox (Oral): 800 mg 4 times daily for 5 days in adults and adolescents over 40 kg.

Herpes Simplex Encephalitis (IV): 10 mg/kg every 8 hours for 10–14 days, infused over 1 hour.

Immunocompromised Patients (IV): 5–10 mg/kg every 8 hours for 7–14 days, depending on infection severity.

Dosage for Children

Chickenpox (Oral, 2–12 years or <40 kg): 20 mg/kg 4 times daily (max 800 mg/dose) for 5 days.

Herpes Simplex (Oral, >2 years): 200–400 mg 5 times daily for 5–10 days, based on body weight and severity.

Neonatal Herpes (IV):

• 10–20 mg/kg every 8 hours for 14–21 days, under neonatal specialist care.
• Not recommended under 2 years for oral use without pediatric approval.

Dosage for Pregnant Women

Pregnancy Category B: Limited data; use only if benefits outweigh risks (e.g., severe HSV). Consult an obstetrician, with fetal monitoring for high-dose IV use.

Dosage Adjustments

Renal Impairment:

• CrCl 25–50 mL/min: Reduce IV to 5–10 mg/kg every 12 hours; oral to 200 mg 4 times daily.
• CrCl 10–25 mL/min: Reduce IV to 5–10 mg/kg every 24 hours; oral to 200 mg 3 times daily.
• CrCl <10 mL/min: Reduce IV to 2.5–5 mg/kg every 24 hours; oral to 200 mg twice daily.

Hepatic Impairment: No adjustment needed unless severe; monitor for toxicity.

Elderly: Start with lower doses (e.g., 200 mg 4 times daily); increase if tolerated, with renal function monitoring.

Obese Patients: Base dose on ideal body weight to avoid overdosage.

Additional Considerations

• Take oral forms with or without food; maintain hydration to prevent crystalluria.
• IV administration requires slow infusion to minimize renal irritation.

How to Use Acyclovir

Administration:

• Oral: Swallow tablets whole with a full glass of water, with or without food; use a dosing spoon for suspension (200 mg/5 mL).
• Topical: Apply a thin layer of 5% cream to affected areas (e.g., lips, genitals) 5 times daily for 4 days, using a clean finger or cotton swab, avoiding eye contact.
• IV: Reconstitute 500 mg vial with 10 mL sterile water, dilute in 100–250 mL saline or D5W, and infuse over 1 hour via a controlled pump, using a 0.45–0.6 micron filter.
• Ophthalmic: Apply 1 cm ribbon of ointment to the lower conjunctival sac 5 times daily (every 3 hours) until healed, then 3 times daily for 7 days.

Timing: Administer at consistent intervals (e.g., every 4–6 hours while awake for oral), starting therapy within 72 hours of symptom onset for best results.

Monitoring: Watch for rash, swelling, or changes in urination; check for signs of renal dysfunction (e.g., reduced output).

Additional Tips:

• Store tablets at 15–25°C (59–77°F), cream at 15–30°C (59–86°F), and IV vials at 2–8°C (36–46°F).
• Avoid touching topical application sites with hands post-use; wash hands thoroughly.
• Report severe itching, blistering, or signs of kidney issues (e.g., flank pain) immediately.

Contraindications for Acyclovir

Hypersensitivity: Patients with a known allergy to Acyclovir, valacyclovir, or any component (e.g., propylene glycol in IV formulation).

Severe Renal Failure: Avoid if CrCl <10 mL/min without dialysis adjustment due to accumulation risk.

Neonates (Oral): Contraindicated under 2 years for oral use due to dosing challenges.

Concurrent Nephrotoxic Drugs: Avoid with high-dose aminoglycosides or cisplatin without renal monitoring.

Acute Dehydration: Contraindicated without rehydration due to crystalluria risk.

Warnings & Precautions for Acyclovir

General Warnings

Renal Toxicity: Risk of acute kidney injury from crystalluria; ensure adequate hydration (2–3 L/day) during IV use.

Neurologic Effects: Rare encephalopathy or confusion, especially in elderly or renal-impaired patients; monitor mental status.

Thrombotic Thrombocytopenic Purpura/Hemolytic Uremic Syndrome (TTP/HUS): Rare but serious; discontinue if signs appear.

Resistance: Potential viral resistance in immunocompromised patients with prolonged use; consider alternative antivirals.

Hypersensitivity Reactions: May cause anaphylaxis or angioedema; stop if severe.

Additional Warnings

Hepatotoxicity: Elevated liver enzymes with high-dose IV; monitor monthly in long-term use.

Bone Marrow Suppression: Rare leukopenia or thrombocytopenia; check blood counts in immunocompromised patients.

Ocular Effects: Corneal toxicity with ophthalmic use; avoid overuse and monitor vision.

Pregnancy Risks: Category B, but high-dose IV linked to fetal harm; use cautiously.

Lactation: Excreted in breast milk; monitor infant if breastfeeding during therapy.

Use in Specific Populations

Pregnancy: Category B; use only if needed, with fetal monitoring for IV doses.

Breastfeeding: Excreted in milk; weigh benefits vs. risks, monitoring infant.

Elderly: Higher risk of renal and neurologic effects; adjust dose and hydrate.

Children: Safe for oral use over 2 years; IV use requires specialist oversight.

Renal/Hepatic Impairment: Adjust dose; avoid in severe renal failure.

Additional Precautions

• Inform your doctor about kidney disease, neurological conditions, or dehydration before starting this medication.
• Avoid abrupt cessation in suppressive therapy; taper under supervision.

Overdose and Management of Acyclovir

Overdose Symptoms

• Renal failure, lethargy, or seizures from crystalluria.
• Severe cases: Coma, metabolic acidosis, or neurotoxicity.
• Nausea, vomiting, or tremor as early signs.
• Confusion or reduced urine output with high doses.

Immediate Actions

Contact the Medical Team: Seek immediate medical help.

Supportive Care: Administer IV fluids to enhance renal clearance, monitor electrolytes, and provide dialysis if needed.

Specific Treatment: Use anticonvulsants for seizures, alkalinize urine to dissolve crystals, or hemodialysis for severe toxicity (e.g., serum levels >20 mg/L).

Monitor: Check renal function, neurologic status, and serum Acyclovir levels for 24–48 hours.

Additional Notes

• Overdose risk increases with rapid IV infusion; use controlled pumps.
• Report persistent symptoms (e.g., severe confusion, oliguria) promptly.

Side Effects of Acyclovir

Common Side Effects

• Nausea (10–20%, manageable with food)
• Diarrhea (5–15%, reduced with hydration)
• Headache (5–10%, alleviated with rest)
• Rash (3–8%, transient with topical use)
• Fatigue (2–6%, common with IV)

These effects may subside with dose adjustment or supportive care.

Serious Side Effects

• Renal: Acute kidney injury, crystalluria, or oliguria.
• Neurologic: Confusion, hallucinations, or seizures.
• Hematologic: Leukopenia, thrombocytopenia, or anemia.
• Hepatic: Jaundice or elevated liver enzymes.
• Allergic: Anaphylaxis, angioedema, or severe rash.

Additional Notes

• Regular monitoring for renal function, blood counts, and neurologic status is advised, especially with IV use.
• Report any unusual symptoms (e.g., vision changes, severe weakness) immediately to a healthcare provider.

Drug Interactions with Acyclovir

This active ingredient may interact with:

Probenecid: Increases Acyclovir levels; reduce dose to prevent toxicity.

Nephrotoxic Drugs (e.g., Ciclosporin): Enhances renal injury risk; monitor creatinine.

Theophylline: May alter clearance; monitor levels.

Zidovudine: Increases neurotoxicity risk; use cautiously.

Immunosuppressants: May reduce efficacy; adjust doses.

Patient Education or Lifestyle

Pharmacokinetics of Acyclovir

Absorption: Oral bioavailability 15–30% (increases with dose); peak at 1.5–2 hours.

Distribution: Volume of distribution ~0.8 L/kg; 9–33% protein-bound, crosses the blood-brain barrier.

Metabolism: Hepatic and intracellular to acyclovir triphosphate via viral thymidine kinase.

Excretion: Primarily renal (60–90% unchanged); half-life 2.5–3.3 hours.

Half-Life: 2.5–3.3 hours, prolonged to 19.5 hours in anuria.

Pharmacodynamics of Acyclovir

This drug exerts its effects by:

Inhibiting viral DNA polymerase after phosphorylation by viral thymidine kinase.

Preventing viral DNA chain elongation, halting replication in HSV and VZV.

Exhibiting selectivity for infected cells, minimizing host cell toxicity.

Demonstrating dose-dependent renal clearance, with toxicity risk at high doses.

Storage of Acyclovir

• Temperature: Store tablets at 15–25°C (59–77°F), cream at 15–30°C (59–86°F), and IV vials at 2–8°C (36–46°F).
• Protection: Keep in original container, away from moisture and light.
• Safety: Store out of reach of children.
• Disposal: Dispose of unused product per local regulations or consult a pharmacist.

Frequently Asked Questions (FAQs) About Acyclovir

Q: What does Acyclovir treat?
A: This medication treats herpes and shingles.

Q: Can this active ingredient cause kidney issues?
A: Yes, renal toxicity may occur; stay hydrated.

Q: Is Acyclovir safe for children?
A: Yes, for 2+ years with a doctor’s guidance.

Q: How is this drug taken?
A: Orally, topically, IV, or ophthalmically, as directed.

Q: How long is Acyclovir treatment?
A: 5–14 days for acute; months for suppression.

Q: Can I use Acyclovir if pregnant?
A: Yes, with caution; consult a doctor.

Regulatory Information for Acyclovir

This medication is approved by:

• U.S. Food and Drug Administration (FDA): Approved in 1982 (Zovirax) for herpes and VZV.
• European Medicines Agency (EMA): Approved for viral infections.
• Other Agencies: Approved globally for herpes and shingles; consult local guidelines.

References

1. U.S. Food and Drug Administration (FDA). (2025). Zovirax (Acyclovir) Prescribing Information.
   • Official FDA documentation detailing the drug’s approved uses, dosage, and safety.
2. European Medicines Agency (EMA). (2025). Acyclovir Summary of Product Characteristics.
   • EMA’s comprehensive information on the medication’s indications and precautions in Europe.
3. National Institutes of Health (NIH). (2025). Acyclovir: MedlinePlus Drug Information.
   • NIH resource providing detailed information on the drug’s uses, side effects, and precautions.
4. World Health Organization (WHO). (2025). WHO Model List of Essential Medicines: Acyclovir.
   • WHO’s inclusion of Acyclovir for viral infections.
5. Journal of Antimicrobial Chemotherapy. (2024). Acyclovir in Herpes Management.
   • Peer-reviewed article on Acyclovir efficacy (note: access may require a subscription).