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Drug dosage identifier

Aciclovir sodium

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Dose and administration

20 mg/kg/dose IV infusion by syringe pump over one hour.

≤29 q12h
30 to 36 q8h
36-41 q8h*
All gestations >28 days chronological age q8h
Postmenstrual age  (weeks) Dosing interval  (hr)
  • * Standard dosing has been "every 8 hours" in this group but recent literature has suggested "every 6 hours can be used in infants 36 - 41 weeks gestation, under 28 days of age" - with monitoring for toxicity (FBC/creatinine - see Special Considerations). Consult with Neonatology Specialist or ID Physician before initiating "every 6 hours" dose interval.
  • Treat disseminated Neonatal herpes simplex virus (HSV) for 21 days if baby has CNS involvement 
  • Treat Varicella zoster virus (VZV) for 7 - 10 days 
  • Double the dose interval for renal failure. 
  • Reduce dose if severe renal failure (serum creatinine greater than 130 umol/L)1,3 


  • Neonatal herpes simplex infections (especially if CNS and pulmonary involvement). 
  • Neonatal varicella zoster infections. 


Hypersensitivity to aciclovir or valaciclovir.


  • Caution in preterm infants, especially extreme immaturity. 
  • Caution in infants with renal, hepatic or electrolyte abnormalities or significant hypoxia.
  • Caution in infants with underlying neurological abnormalities.
  • Maintain adequate hydration. 

Clinical pharmacology

Antiviral agent which is highly active in vitro against herpes simplex (types 1 and 2) and varicella zoster viruses. Preferentially taken up by infected cells and then phosphorylated to the active compound aciclovir triphosphate. Acts as an inhibitor of, and substrate for, the herpes specified DNA polymerase. Prevents further viral DNA synthesis without affecting normal cellular processes. Toxicity to mammalian host cells is low.

Widely distributed throughout the body fluids and tissues. CSF concentrations approximately 50% that of plasma. Low binding (9-24%) to human plasma protein. Eliminated, mainly unchanged via the kidney, primarily by glomerular filtration. Elevated serum concentrations may be reduced by haemodialysis.

Possible adverse effects

  • Increases in liver-related enzymes (reversible)
  • Increase in urea and creatinine - slow infusion over one hour and adequate patient hydration may avoid this.
  • Venous irritation. Inflammation and phlebitis at IV site following extravasation. 
  • Rash
  • Other adverse effects: renal failure, thrombotic thrombocytopenic purpura (TTP)/haemolytic uremic syndrome (HUS). 

Special considerations


  1. Renal function. Check prior to commencing and during therapy. Use a slow infusion rate and maintain adequate hydration to minimise the risk of renal dysfunction and renal crystalluria.
    1. Concomitant nephrotoxic drugs. Consider impact of these on renal function
    2. CNS toxicity. More likely to occur with accumulation of aciclovir due to reduced renal function.
  2. Full Blood count. 
  3. Electrolytes
  4. Liver function tests.
  5. Monitoring for 6 hourly dose interval: 
    Monitor creatinine & urea daily, FBC weekly. Keep patient hydrated and administer dose over 60 minutes.

Resistant viral strains may emerge during long term therapy. There is NO evidence Aciclovir will stop transmission of the virus

Aciclovir (Zovirax®) is licensed in New Zealand for the treatment of Herpes simplex infections in neonates

Management of Aciclovir administration


Aciclovir (Zovirax ®) is sterile white/off-white powder for reconstitution. A 5mg/mL solution has osmolality ~ 289 mOsm/L; pH = 11


Charted on the prescription chart in mg/dose.


Slow IV Infusion over 1 hour

  • Ensure patient is well hydrated before and during administration. This is especially important if there is any degree of renal impairment AND for 6 hourly dose interval.
  • Dilute prior to administration:
  Aciclovir (Zovirax®) 250 mg
Powder Space Nil
Water For Injection 10 mL
  250 mg in 10mL
  • Dilute this further to 5 mg/mL with sodium chloride 0.9%
  • Use a Pall 0.2 micron in-line filter during administration.
  • Administer by slow IV infusion over 1 hour using a syringe pump.
  • Do not use if any visible turbidity or if crystals form before or during infusion. Discard this solution and prepare a fresh solution.
  • Do NOT mix with other drugs, IV solutions, blood or blood products. Flush line with sodium chloride 0.9% before and after infusion
  • Do NOT administer by bolus IV injection, IM or SC.

Nursing considerations

  • Assess IV site carefully before and during infusion of aciclovir. The solution is highly alkaline and extravasation may cause significant tissue damage.
  • Observe for signs of adverse effects.
  • Monitor fluid balance closely, and renal function
  • Not compatible with dopamine, dobutamine and morphine.


  • Ampoules are single-use. Do not store reconstituted solution
  • Do not refrigerate solution as may precipitate.


  1. Sampson MR, Bloom BT, Lenfestey RW, et al. Population pharmacokinetics of intravenous acyclovir in preterm and term infants. Pediatr Infect Dis J. 2014; (33): 42 - 49.
  2. Neonatal Formulary. 6thed. Oxford: Wiley-Blackwell; 2011.
  3. Phelps SJ, Hak EB, Crill CM, editors. Teddy bear book: Pediatric injectable drugs. 8th ed. Bethesda, MD: American Society of Heath-System Pharmacists; 2007.
  4. Zovirax data sheet, Auckland: GlaxoSmith Kline NZ Limited, 2014.
  5. Paediatric Injectable Guidelines 4th ed. Melbourne,The Royal Children's Hospital: 2011.

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Document Control

  • Date last published: 23 August 2015
  • Document type: Drug Dosage Guideline
  • Services responsible: ADHB Pharmacy, Neonatology
  • Editor: Sarah Bellhouse
  • Review frequency: 2 years