What is the appropriate acyclovir oral suspension dosage for a 16 kg child with normal renal function?

Acyclovir Oral Suspension Dosing for a 16 kg Child

For a 16 kg child with normal renal function, administer acyclovir oral suspension 320 mg (20 mg/kg) four times daily, with the specific indication determining treatment duration. 1

Weight-Based Dosing Calculation

• Standard pediatric oral dose: 20 mg/kg per dose, administered four times daily 1, 2
• For this 16 kg child: 20 mg/kg × 16 kg = 320 mg per dose
• Maximum single dose: 800 mg (not applicable to this patient) 1, 2
• Total daily dose: 1,280 mg/day (320 mg × 4 doses)

Indication-Specific Duration

Varicella (Chickenpox)

• Duration: 7–10 days or until no new lesions appear for 48 hours 1, 2
• Timing: Most effective when initiated within 24 hours of rash onset 2
• Applies to: Children with mild to moderate immunosuppression (CDC immunologic categories 1 and 2) 1

Herpes Simplex Virus (HSV) Infections

• Neonatal skin/eye/mouth disease: 20 mg/kg IV three times daily for 14 days (not oral) 1
• Recurrent genital herpes (adolescents): Multiple oral regimens available, but this child's age makes HSV less likely 3

Herpes Zoster (Shingles)

• Duration: 7–10 days 1
• Same dose: 20 mg/kg (max 800 mg) four times daily 1

Critical Considerations for This Weight Category

This 16 kg child falls just above the ≤15 kg threshold used in some dosing algorithms, but weight-based calculation (20 mg/kg) takes precedence over categorical dosing. 1, 2 The 320 mg dose is well below the 800 mg maximum, ensuring safety while maintaining therapeutic efficacy.

Severe Disease or Immunocompromised Status

If this child has severe immunosuppression (CDC category 3) or severe/disseminated disease:

• Switch to IV acyclovir: 10 mg/kg every 8 hours 1
• Alternative IV dosing (for children >1 year): 500 mg/m² every 8 hours 1, 3
• Duration: 7–10 days IV, then may transition to oral therapy 1

Pharmacokinetic Rationale

• Bioavailability: Approximately 12% for oral acyclovir 4
• Half-life: 2.5–2.6 hours in children 6 months to 7 years 5, 4, 6
• Target concentration: Trough levels should remain above 0.56 mg/L for HSV or 1.125 mg/L for VZV 7
• Renal clearance: Acyclovir clearance is directly related to estimated glomerular filtration rate (eGFR) and body surface area 4, 7

Common Pitfalls to Avoid

• Do not round to fixed adult doses: A 16 kg child requires 320 mg, not 400 mg or 800 mg 1, 2
• Do not underdose: Using 15 mg/kg instead of 20 mg/kg may result in subtherapeutic levels for VZV 4
• Do not delay treatment: Efficacy decreases significantly if treatment is not started within 24–72 hours of symptom onset 2, 5
• Ensure adequate hydration: Acyclovir can crystallize in renal tubules; maintain good fluid intake throughout treatment 3

Renal Function Monitoring

• Normal renal function: No dose adjustment needed 5, 7
• Impaired renal function: Reduce dose and/or extend dosing interval based on creatinine clearance 5
• Augmented renal clearance (eGFR >250 mL/min/1.73 m²): May require increased dosing frequency (consider 15 mg/kg every 6 hours instead of 20 mg/kg every 8 hours for severe infections) 7

Administration Instructions

• May be given with or without food (food does not affect absorption) 5
• Use calibrated oral dosing syringe to ensure accurate measurement of the suspension
• Shake suspension well before each dose
• Complete the full course even if symptoms improve earlier 3

Expected Clinical Response

• Improvement should occur within 48–72 hours of initiating therapy 3
• Monitor for: Reduction in new lesion formation, decreased pain, and lesion crusting/healing 5
• Does not eradicate latent virus: Recurrences may still occur after treatment completion 3