What is the recommended dose of acyclovir (antiviral medication) for the treatment of varicella (chickenpox)?

Acyclovir Dosing for Varicella (Chickenpox)

For the treatment of varicella (chickenpox), the recommended dose of acyclovir is 800 mg orally four times daily for 5 days in adults and children over 40 kg, and 20 mg/kg orally four times daily for 5 days in children under 40 kg. 1

Dosing Recommendations by Age and Weight

Children (2 years and older)

• Standard dose: 20 mg/kg per dose orally 4 times daily (total 80 mg/kg/day) for 5 days 1
• Maximum dose: 800 mg per dose (for children >40 kg)
• Timing: Treatment should be initiated within 24 hours of rash onset for maximum effectiveness 2

Adults and Children >40 kg

• Standard dose: 800 mg orally 4 times daily for 5 days 1
• Timing: Treatment should be initiated within 24 hours of rash onset for maximum effectiveness 2

Special Populations

Immunocompromised Patients

• Children with compromised immunity: Intravenous acyclovir is preferred 3
• Severe disease: 10 mg/kg IV every 8 hours for 7-10 days 3

Patients with Renal Impairment

Dose adjustment is required based on creatinine clearance:

• Creatinine clearance >25 mL/min: 800 mg every 4 hours, 5 times daily
• Creatinine clearance 10-25 mL/min: 800 mg every 8 hours
• Creatinine clearance <10 mL/min: 800 mg every 12 hours 1

Clinical Efficacy

Acyclovir treatment for varicella has been shown to:

• Reduce the number of lesions (mean 294 vs 347 in placebo) 4
• Accelerate healing and reduce new lesion formation 4
• Decrease duration of fever and constitutional symptoms 4
• Be particularly beneficial in adolescents, who typically experience more severe disease than younger children 5

Treatment Considerations

• Treatment must be initiated within 24 hours of rash onset for optimal efficacy 2
• Acyclovir does not significantly reduce complications in otherwise healthy children 2
• For immunocompromised children, oral acyclovir at 800 mg five times daily has been shown to prevent dissemination of varicella 6

Common Pitfalls and Caveats

1. Delayed initiation: Acyclovir should be started within 24 hours of rash onset. There is limited evidence for efficacy when started later 1, 2

2. Inadequate dosing: Underdosing may lead to treatment failure, particularly in immunocompromised patients

3. Renal function assessment: Failure to adjust dosing in patients with renal impairment can lead to toxicity 1

4. Inappropriate use: Not all cases of varicella require antiviral treatment. The CDC recommends treatment primarily for:

   • Individuals >12 years old
   • Those with chronic skin or lung disorders
   • Patients on long-term salicylate therapy
   • Individuals receiving corticosteroids
   • Immunocompromised patients 2

5. Hydration: Ensuring adequate hydration is important, especially with the higher doses used for varicella treatment

By following these dosing guidelines and considering the specific patient factors, acyclovir can effectively reduce the severity and duration of varicella infection, particularly in high-risk populations.