Acyclovir Pediatric Dose — Antiviral Dosing Guide
Acyclovir is a synthetic purine nucleoside analogue antiviral that inhibits viral DNA polymerase after phosphorylation by viral thymidine kinase. It is the cornerstone agent for treatment of herpes simplex virus (HSV) and varicella-zoster virus (VZV) infections in pediatric patients, including neonatal HSV encephalitis, disseminated disease, and immunocompromised host infections.
Pediatric Dosing
Weight-Based IV Dosing
- Neonates and Infants: 20 mg/kg/dose IV every 8 hours
- Adolescents: 10 mg/kg/dose IV every 8 hours
Worked example (Neonate): For a 3.5 kg neonate: 3.5 × 20 mg/kg = 70 mg IV every 8 hours.
Worked example (Adolescent): For a 50 kg adolescent: 50 × 10 mg/kg = 500 mg IV every 8 hours.
Body Surface Area (BSA)-Based IV Dosing
- VZV: 500 mg/m²/dose IV every 8 hours
- HSV: 250 mg/m²/dose IV every 8 hours
Worked example (VZV): For a child with BSA of 0.8 m²: 0.8 × 500 mg/m² = 400 mg IV every 8 hours.
Oral Dosing
- 750 mg/m²/dose PO every 12 hours
Worked example: For a child with BSA of 1.0 m²: 1.0 × 750 mg/m² = 750 mg PO every 12 hours. Consult institutional protocol for maximum single doses and duration by indication.
Indications and Clinical Context
Acyclovir is indicated for treatment of HSV and VZV infections across the pediatric age spectrum. In neonates and young infants, IV acyclovir is the standard of care for HSV infections including encephalitis, disseminated disease, and skin-eye-mouth (SEM) disease, where higher weight-based dosing (20 mg/kg/dose) is employed to achieve adequate CNS penetration. In adolescents, the 10 mg/kg/dose regimen aligns with adult dosing principles for serious herpetic infections.
BSA-based dosing (500 mg/m²/dose for VZV; 250 mg/m²/dose for HSV) is commonly applied in older pediatric and immunocompromised patients and is consistent with dosing frameworks referenced in established pediatric infectious disease guidelines. Oral acyclovir at 750 mg/m²/dose every 12 hours may be appropriate for outpatient management or step-down therapy in select, clinically stable patients at the discretion of the treating clinician.
Administration and Monitoring
IV acyclovir should be administered as a slow intravenous infusion over at least 60 minutes to minimize the risk of crystalline nephropathy from precipitation in renal tubules. Ensure adequate hydration before and during infusion. The IV/IO route is preferred for serious or disseminated infections; oral formulations are reserved for mild-to-moderate disease or outpatient step-down therapy. Consult institutional protocol for compatible diluents and maximum concentration limits.
- Renal monitoring: Assess serum creatinine and urine output regularly, particularly in neonates and patients with baseline renal impairment; dose adjustment is required for renal dysfunction.
- Neurotoxicity: Monitor for encephalopathy, tremor, or agitation, especially at higher doses.
- Phlebitis: Use appropriately diluted solutions to reduce risk of local irritation at the infusion site.
- Contraindications: Known hypersensitivity to acyclovir or valacyclovir.
Disclaimer: This article is an educational reference summarizing standard pediatric dosing values. It is not a substitute for clinical judgment. Always verify doses against institutional protocols, the current edition of authoritative references (e.g., Lexicomp, Harriet Lane Handbook, PALS guidelines), the patient’s accurate weight, and any patient-specific factors (renal/hepatic function, allergies, comedications) before administration.