Acyclovir (aciclovir) Pediatric Dose Calculator
Weight-based acyclovir dosing for children — 20 mg/kg/dose · four times daily · max 800 mg/dose, 3200 mg/day. Enter age and weight for the dose in mg and syrup mL, tablets or injection volume.
Pediatric dosing
Chickenpox (varicella) — when treatment is indicated
Herpes simplex gingivostomatitis / mucocutaneous HSV
Neonatal herpes simplex (suspected or confirmed) — IV Hospital
Acyclovir (aciclovir) dose chart by age and weight
Chickenpox (varicella) — when treatment is indicated. Weights are WHO/IAP reference medians for age — always dose on the measured weight.
| Age | Weight | Dose (mg) | Suspension 200 mg/5 mL | Suspension 400 mg/5 mL | Frequency |
|---|---|---|---|---|---|
| 15 days | 3.8 kg | Below minimum age | |||
| 1 month | 4.3 kg | Below minimum age | |||
| 3 months | 6.1 kg | Below minimum age | |||
| 6 months | 7.6 kg | Below minimum age | |||
| 9 months | 8.6 kg | Below minimum age | |||
| 1 year | 9.3 kg | Below minimum age | |||
| 18 months | 10.6 kg | Below minimum age | |||
| 2 years | 11.8 kg | 236 mg | 5.9 mL | 3 mL | Four times daily |
| 3 years | 14.1 kg | 282 mg | 7.1 mL | 3.5 mL | Four times daily |
| 4 years | 16.2 kg | 324 mg | 8.1 mL | 4.1 mL | Four times daily |
| 5 years | 17.5 kg | 350 mg | 8.8 mL | 4.4 mL | Four times daily |
| 6 years | 19 kg | 380 mg | 9.5 mL | 4.8 mL | Four times daily |
| 8 years | 24.4 kg | 488 mg | 12 mL | 6.1 mL | Four times daily |
| 10 years | 31.1 kg | 622 mg | 15.5 mL | 7.8 mL | Four times daily |
| 12 years | 39.4 kg | 788 mg | 19.5 mL | 9.9 mL | Four times daily |
Strengths in the calculator
- Suspension 200 mg/5 mL (Oral)
- Suspension 400 mg/5 mL (Oral)
- Tablet 200 mg (dispersible) (Oral)
- Tablet 400 mg (dispersible) (Oral)
- Tablet 800 mg (dispersible) (Oral)
- 250 mg vial + 10 mL = 25 mg/mL (dilute further to ≤5 mg/mL) (Intravenous) — Infuse over at least 1 hour; keep the child well hydrated.
Different strength on your bottle? Use “Different strength on the bottle?” under the result.
Safety
Contraindications and cautions
- Renal impairment: reduce the dose and ensure good hydration (risk of crystal nephropathy).
Pregnancy and breastfeeding
Legacy FDA category B. Widely used in pregnancy (primary genital herpes, varicella); no increase in birth defects in large registries.
Compatible.
Clinical notes
Oral bioavailability is low (15–30%) — oral treatment is not adequate for encephalitis, neonatal or disseminated HSV, or varicella in immunocompromised children.
Adult and adolescent (≥40 kg) dose
Herpes simplex: 400 mg three times daily; varicella/zoster: 800 mg five times daily — Five times daily for 7 days (varicella/zoster) (max 800 mg per dose).
Other names and brands
Also known as aciclovir, acyclovir.
- India: Acivir, Zovirax
- USA: Zovirax
- UK: Zovirax
Brand examples only — products and strengths vary by country. Always check the label.
Frequently asked questions
What is the acyclovir dose for children?
Chickenpox (varicella) — when treatment is indicated: 20 mg/kg/dose · four times daily · max 800 mg/dose, 3200 mg/day. Usual duration: 5 days. Always use the child's measured weight and check the strength on the bottle.
How many mL of suspension 200 mg/5 mL for an 11.8 kg child?
For chickenpox (varicella) — when treatment is indicated, an 11.8 kg child (about 2 years) needs 236 mg per dose — 5.9 mL of Suspension 200 mg/5 mL, four times daily. Recalculate with the child's actual weight.
From what age can acyclovir be given?
Age range in PediaRx: Oral: ≥3 months (varicella ≥2 years) · IV neonatal HSV: hospital. Each indication can have its own age and weight limits, shown with its regimen.
Is acyclovir safe in pregnancy?
Legacy FDA category B. Widely used in pregnancy (primary genital herpes, varicella); no increase in birth defects in large registries.
Sources and editorial process
- Red Book: Report of the Committee on Infectious Diseases — Herpes simplex and Varicella-zoster chapters — American Academy of Pediatrics
- BNF for Children — Aciclovir — NICE / BMJ Group / Royal Pharmaceutical Society
- Acyclovir oral suspension and tablets — US prescribing information — DailyMed (U.S. National Library of Medicine)
Dosing data last updated 2026-09-28. PediaRx is built and maintained by Dr. Shounak Pal, MBBS (Medical Officer, Government of West Bengal, India — founder and developer of PediaRx). Every regimen is encoded with explicit units, maximum doses and age/weight limits and is checked by automated tests before publication. Report an error: hello@pediarx.com.
Clinical disclaimer: reference tool for qualified health professionals. Verify every dose against current guidance and the product label before prescribing.
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