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Antiviral — HSV Encephalitis / Neonatal Herpes / VZV in Immunocompromised

Aciclovir (Paediatric)

Brand names: Zovirax

This page covers aciclovir use in children — an antiviral active against herpes simplex and varicella-zoster, used for conditions such as neonatal herpes, herpes encephalitis, chickenpox and zoster.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

Aciclovir is phosphorylated by viral thymidine kinase and cellular enzymes to a triphosphate that inhibits viral DNA polymerase and terminates viral DNA chain elongation.

Prescribing in practice

  • In children, doses must be calculated against weight or body-surface area using a children's formulary, and intravenous aciclovir requires adequate hydration to prevent crystal nephropathy and acute kidney injury.
  • Dose adjustment is needed in renal impairment, and infusion should be given slowly rather than as a bolus.
  • Neurotoxicity such as confusion or tremor can occur, particularly with high plasma levels or impaired renal function.

Monitoring

Monitor renal function and hydration during intravenous therapy, and observe for neurological side effects.

Counselling the patient

  • Ensure the child drinks well or receives fluids during treatment.
  • Starting treatment early gives the best chance of benefit.
  • Report reduced urine output, drowsiness or unusual behaviour.

Evidence & guidelines

Aciclovir is the established first-line antiviral for serious paediatric herpes infections in UK guidance.

Reference: NICE NG41 (Meningitis); PHE Neonatal Herpes Guidelines; BPSU/BPNG Neonatal Herpes Simplex Guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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