What is the recommended dose of acyclovir (antiviral medication) for treating Herpes Simplex Virus (HSV) infections in pediatric patients?

Pediatric Acyclovir Dosing for HSV Infections

The recommended acyclovir dosage for pediatric HSV infections varies by clinical presentation, with oral acyclovir at 20 mg/kg/dose (maximum 400 mg/dose) three times daily for 5-14 days being appropriate for mild to moderate mucocutaneous infections, while severe or CNS infections require intravenous therapy at 10-20 mg/kg every 8 hours. 1, 2

Dosing by Clinical Presentation

Neonatal HSV Infections (Birth to 3 months)

• CNS or disseminated disease: 20 mg/kg IV every 8 hours for 21 days 1
• Skin, eye, or mouth disease: 20 mg/kg IV every 8 hours for 14 days 1

Children Outside Neonatal Period

• CNS or disseminated disease: 10 mg/kg IV every 8 hours for 21 days 1
• Mild gingivostomatitis: 20 mg/kg (max 400 mg/dose) orally 3 times daily for 5-10 days 1, 3
• Moderate to severe gingivostomatitis:
  • Initial: 5-10 mg/kg IV every 8 hours 1
  • Transition to oral therapy when lesions begin to regress 1

Genital Herpes

• Children <45 kg: 20 mg/kg (max 400 mg/dose) orally 3 times daily for 5-14 days 1
• Adolescents/Adults: 400 mg orally twice daily for 5-14 days 1

Route of Administration Considerations

Intravenous Administration

• Must be administered at a constant rate over 1 hour 2
• Avoid rapid or bolus injection 2
• Maximum dose should not exceed 20 mg/kg every 8 hours for any patient 2

Oral Administration

• Bioavailability of oral acyclovir is approximately 12% 4
• Elimination half-life decreases sharply during the first month after birth (from 10-15 hours to 2.5 hours) 4

Special Populations

Renal Impairment

Dosage adjustment is necessary based on creatinine clearance 2:

• CrCl >50 mL/min: 100% of dose every 8 hours
• CrCl 25-50 mL/min: 100% of dose every 12 hours
• CrCl 10-25 mL/min: 100% of dose every 24 hours
• CrCl 0-10 mL/min: 50% of dose every 24 hours

Augmented Renal Clearance

• Children with augmented renal clearance (eGFR >250 mL/min/1.73m²) may require higher doses (15-20 mg/kg every 6 hours) 5

Duration of Therapy

• Mucocutaneous infections: 5-14 days 1, 2
• CNS involvement: 21 days 1
• Continue treatment until complete healing of lesions 3
• For HSV encephalitis, repeat CSF HSV DNA PCR at days 19-21 of therapy; do not stop acyclovir until repeat CSF HSV DNA PCR is negative 1

Alternative Antiviral Options

Acyclovir-Resistant HSV

• Foscarnet: 40 mg/kg IV every 8 hours or 60 mg/kg IV every 12 hours 1

Older Children and Adolescents

• Valacyclovir may be used in older children able to receive adult dosing (1 g orally twice daily) 1
• Famciclovir may be used in adolescents (500 mg orally twice daily) 1

Clinical Pearls and Pitfalls

1. Early initiation: Treatment should be started as early as possible following onset of signs and symptoms for maximum efficacy 2, 6

2. Weight-based dosing: Proper weight-based dosing is essential to prevent subtherapeutic levels, with adjustment as the child grows 3

3. Hydration: Maintain adequate hydration during treatment to reduce the risk of nephropathy 3

4. Monitoring: Monitor renal function during treatment, especially with prolonged courses 3

5. Transition criteria: Switch from IV to oral therapy when clinical improvement is evident, lesions begin to regress, and the patient can tolerate oral medications 3

By following these evidence-based dosing recommendations, clinicians can effectively manage HSV infections in pediatric patients while minimizing the risk of treatment failure and adverse effects.