What is the recommended dose of acyclovir (antiviral medication) for a 4-year-old child (YOM - Years Of age Male/Female) weighing 19.6kg with simplex dermatitis, likely due to herpes simplex virus infection?

Acyclovir Dosing for a 4-Year-Old with Herpes Simplex Dermatitis

For a 4-year-old child weighing 19.6kg with herpes simplex dermatitis, the recommended dose of acyclovir is 20 mg/kg body weight (maximum 400 mg/dose) per dose orally 3 times daily for 5-10 days. 1

Dosage Calculation

• Based on the child's weight of 19.6kg:
  • 20 mg/kg × 19.6kg = 392 mg per dose 1
  • This is below the maximum dose of 400 mg per dose 1
  • Administer three times daily for 5-10 days 1

Treatment Considerations

Route of Administration

• Oral acyclovir is appropriate for mild to moderate herpes simplex dermatitis 1
• Intravenous acyclovir should be considered only if:
  • The infection is severe or disseminated 1
  • The child is unable to tolerate oral medication 1
  • The child is immunocompromised 1

Duration of Treatment

• For mild symptomatic herpes simplex infections: 5-10 days of treatment 1
• Treatment should continue until lesions completely heal 1

Monitoring During Treatment

• Monitor renal function, especially if treatment extends beyond 5 days 1
• Watch for potential neutropenia, which can occur in up to 46% of children on prolonged acyclovir therapy 1
• Ensure adequate hydration to prevent crystalluria and obstructive nephropathy 1

Special Considerations

Alternative Medications

• Valacyclovir could be considered for older children who can receive adult dosing, but no pediatric preparation exists and data on dosing in children are limited 1
• Famciclovir is not recommended as no pediatric preparation exists 1

Treatment for Recurrent Infections

• For frequent or severe recurrences: Consider prophylactic acyclovir at 20 mg/kg body weight (max 400 mg/dose) orally twice daily 1

Potential Adverse Effects

• Common: Nausea, vomiting, diarrhea 1
• Less common but important: Renal toxicity, phlebitis (with IV administration), rash 1
• Rare: Neutropenia, especially with prolonged use 1

Clinical Pearls

• Acyclovir is primarily excreted by the kidney; dose adjustment is needed in patients with renal insufficiency 1
• Early initiation of treatment maximizes therapeutic benefit 2
• Acyclovir therapy does not eliminate latent virus or prevent subsequent recurrences 3
• The risk of resistance remains very low (<0.5%) in immunocompetent patients 4