Acyclovir Drug Profile

What is Acyclovir?

Acyclovir is an antiviral medication that belongs to the class of drugs known as nucleoside analogues. It is primarily used to treat infections caused by herpes viruses, including genital herpes, cold sores, shingles, and chickenpox. Acyclovir was one of the first effective antiviral medications developed and remains a cornerstone treatment for herpes virus infections.

Uses

Acyclovir is approved for several viral infections:

• Genital herpes: Both initial outbreaks and recurrent episodes, as well as suppressive therapy to reduce frequency of outbreaks
• Cold sores (oral herpes): Treatment of herpes simplex virus infections around the mouth and lips
• Shingles (herpes zoster): Treatment of the painful rash caused by reactivation of the varicella-zoster virus
• Chickenpox (varicella): Treatment in children and adults, particularly those at higher risk for complications
• Herpes simplex encephalitis: Serious brain infection caused by herpes simplex virus

How it works

Acyclovir works by mimicking one of the building blocks that viruses need to replicate their genetic material. Once inside virus-infected cells, acyclovir is converted to its active form and interferes with the virus’s ability to copy itself. This stops the virus from spreading to new cells and helps the body’s immune system control the infection more effectively.

Side effects

Common side effects include:

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• Nausea and vomiting
• Diarrhea
• Headache
• Dizziness
• Fatigue
• Skin rash or itching
• Pain or irritation at injection site (IV form)
• Abdominal pain

Serious side effects that require immediate medical attention:

• Kidney problems, including decreased urination or blood in urine
• Severe allergic reactions with difficulty breathing or swallowing
• Neurological effects such as confusion, hallucinations, or seizures
• Severe skin reactions or widespread rash
• Signs of thrombotic thrombocytopenic purpura (unusual bruising or bleeding)

Warnings and precautions

Several important safety considerations apply to acyclovir use:

• Kidney function: Patients with kidney disease require dose adjustments, and adequate hydration is essential to prevent kidney damage, especially with IV administration
• Pregnancy and breastfeeding: Generally considered safe during pregnancy (Category B) when benefits outweigh risks, and small amounts pass into breast milk
• Elderly patients: May be at higher risk for kidney problems and neurological side effects, requiring careful monitoring and possible dose adjustments
• Immunocompromised patients: While often prescribed for this population, these patients may require higher doses and longer treatment duration
• Dehydration risk: Maintaining adequate fluid intake is crucial, particularly with oral and IV forms

Interactions

Acyclovir can interact with several medications:

• Probenecid: Increases acyclovir levels in the blood by reducing kidney elimination
• Nephrotoxic drugs (aminoglycosides, amphotericin B): May increase risk of kidney damage when used together
• Mycophenolate mofetil: Both drugs may have increased concentrations when used concurrently
• Theophylline: Acyclovir may increase theophylline levels, requiring monitoring
• Zidovudine: May increase risk of drowsiness and fatigue
• Cimetidine: May increase acyclovir levels by reducing kidney clearance
• Tenofovir: Potential for increased kidney toxicity when used together
• Varicella virus vaccine: Acyclovir may reduce vaccine effectiveness

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Dosage

Acyclovir dosages vary significantly based on the condition being treated, severity of infection, and patient factors. Typical adult dosages include:

• Genital herpes (initial episode): 400 mg three times daily or 200 mg five times daily for 7-10 days
• Genital herpes (recurrent episodes): 400 mg three times daily for 5 days
• Suppressive therapy: 400 mg twice daily
• Shingles: 800 mg five times daily for 7-10 days
• Chickenpox: 800 mg four times daily for 5 days

Dosages must be adjusted for patients with kidney problems, and IV formulations have different dosing schedules. All dosing should be determined and monitored by a qualified healthcare provider based on individual patient needs and medical history.

Sources: FDA DailyMed drug labels (public domain), BNF, WHO Essential Medicines List. This article is for informational purposes only and does not constitute medical advice. Always consult your healthcare provider before starting or stopping any medication.

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