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PubMed This is a summary of 15 peer-reviewed journal articles Updated
Pediatrics · Neonatal Herpes Simplex Virus

Acute Treatment: The Role of IV Acyclovir

At a Glance

Intravenous (IV) acyclovir is the standard, life-saving treatment for neonatal HSV. It is started immediately upon suspicion of the virus to prevent organ and brain damage. Treatment lasts 14 to 21 days depending on the infection type, with close monitoring for kidney and blood cell health.

When a baby is suspected of having neonatal herpes simplex virus (HSV), time is the most important factor. Doctors do not wait for laboratory confirmation before beginning treatment. Instead, they start medication empirically—meaning they treat based on clinical suspicion to give the baby the best possible head start [1][2].

The Standard of Care: High-Dose Acyclovir

The gold standard for treating neonatal HSV is intravenous (IV) acyclovir [3][4]. Because the virus can be aggressive in newborns, the dose used is much higher than what might be used for an adult with a cold sore.

  • The Dose: The standard regimen is 20 mg/kg per dose, given every 8 hours [3][4].
  • The Method: The medication must be given through an IV to ensure it reaches the bloodstream and the brain immediately.

How Acyclovir Works

Acyclovir is a “pro-drug,” which means it enters the body in an inactive form. It only becomes “activated” once it encounters the herpes virus [5].

  • Targeting the Virus: Once activated, the drug specifically targets an enzyme the virus uses to copy its DNA (viral DNA polymerase) [5][6].
  • Stopping the Spread: By “jamming” this copying machine, acyclovir prevents the virus from making new copies of itself. This stops the infection from spreading further into the baby’s organs or brain [6].

Treatment Timelines

The length of time your baby will need IV acyclovir depends entirely on which classification of the disease they have:

  • Skin, Eye, and Mouth (SEM) Disease: 14 days of IV treatment [4][7].
  • Central Nervous System (CNS) Disease: 21 days of IV treatment [4][8].
  • Disseminated (Systemic) Disease: 21 days of IV treatment [4][7].

For babies with CNS disease, doctors will often perform a repeat lumbar puncture (spinal tap) near the end of the 21 days to ensure the virus is no longer detectable in the brain fluid before stopping the IV medication [8].

Why “Wait and See” is Not an Option

Delayed treatment is the single biggest risk factor for poor outcomes in neonatal HSV [1].

  1. Rapid Progression: In newborns, HSV can move from a simple skin blister to a brain or whole-body infection in a matter of hours [9].
  2. Organ Protection: Starting acyclovir early helps protect the liver, lungs, and brain from the inflammatory damage the virus causes [10][11].

Monitoring During Treatment

While acyclovir is life-saving, high doses require careful monitoring by the NICU team:

  • Kidney Health: Acyclovir can sometimes cause crystals to form in the kidneys. To prevent this, the team will ensure your baby is well-hydrated with IV fluids and will regularly check blood markers like creatinine [12][13].
  • Neutrophil Count: In some babies, high-dose acyclovir can lower the count of a type of white blood cell called neutrophils, which help fight infection. This is monitored through regular blood tests (CBC) [14].
  • IV Site: The medication can be irritating to small veins. Nurses will check the IV site frequently for any signs of extravasation (when medicine leaks outside the vein into the tissue), which can look like swelling, cold skin, or a white patch around the IV site [15]. If you notice these signs, notify a nurse immediately.

Common questions in this guide

Why did the doctor start my baby on acyclovir before the herpes test results came back?
Doctors start IV acyclovir immediately based on clinical suspicion because neonatal HSV can progress rapidly. Delayed treatment is the biggest risk factor for poor outcomes, so early treatment helps protect your baby's organs and brain while waiting for lab tests.
How long will my baby need to receive IV acyclovir?
The treatment duration depends on the extent of the infection. Babies with skin, eye, and mouth (SEM) disease usually receive 14 days of IV treatment, while those with central nervous system (CNS) or disseminated disease require 21 days.
How is acyclovir given to newborns?
Acyclovir must be given intravenously (through an IV) to ensure it reaches the baby's bloodstream and brain immediately. The medication is given in high doses every 8 hours.
What side effects will the NICU team monitor for while my baby is on acyclovir?
The medical team will closely monitor your baby's kidney function and hydration, as the medication can sometimes cause crystals in the kidneys. They will also check white blood cell counts and watch the IV site for signs of irritation or medication leakage.
Will my baby need another spinal tap before finishing treatment?
If your baby has central nervous system (CNS) disease, doctors will often perform a repeat lumbar puncture near the end of the 21-day treatment. This ensures the virus is no longer detectable in the brain fluid before safely stopping the medication.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.At what exact time was my baby's first dose of acyclovir administered?
  2. 2.What dose is my baby receiving, and is it adjusted for their weight and kidney function?
  3. 3.Are you monitoring my baby's kidney function and white blood cell count (ANC) while they are on this high-dose medication?
  4. 4.If my baby has CNS disease, will they need a repeat lumbar puncture before we finish the 21-day course?
  5. 5.How is the IV site being monitored to prevent skin irritation or 'extravasation' from the medication?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (15)
  1. 1

    Basics of Neonatal Herpes Simplex Virus.

    Jones JV, Falke M

    Neonatal network : NN 2026; (45(1)):57-62 doi:10.1891/NN-2025-0046.

    PMID: 41748206
  2. 2

    Neonatal herpes simplex virus infection combined with neonatal lupus erythematosus: a case reported.

    Jiang H, Qiu H, Wang M, et al.

    Frontiers in pediatrics 2025; (13()):1592459 doi:10.3389/fped.2025.1592459.

    PMID: 40574945
  3. 3

    A Rare Case of Neonatal Disseminated Herpes Simplex Virus (HSV) With Concomitant Methicillin-Sensitive Staphylococcus aureus (MSSA) Bacteremia.

    Sykes SR, Sharpe EL

    Advances in neonatal care : official journal of the National Association of Neonatal Nurses 2022; (22(5)):400-407 doi:10.1097/ANC.0000000000000949.

    PMID: 34596088
  4. 4

    [Neonatal herpes: Epidemiology, clinical manifestations and management. Guidelines for clinical practice from the French College of Gynecologists and Obstetricians (CNGOF)].

    Renesme L

    Gynecologie, obstetrique, fertilite & senologie 2017; (45(12)):691-704 doi:10.1016/j.gofs.2017.10.005.

    PMID: 29132771
  5. 5

    Antiviral Drugs Against Herpesviruses.

    Piret J, Boivin G

    Advances in experimental medicine and biology 2021; (1322()):1-30 doi:10.1007/978-981-16-0267-2_1.

    PMID: 34258735
  6. 6

    The Anti-Human Immunodeficiency Virus Drug Tenofovir, a Reverse Transcriptase Inhibitor, Also Targets the Herpes Simplex Virus DNA Polymerase.

    Andrei G, Gillemot S, Topalis D, Snoeck R

    The Journal of infectious diseases 2018; (217(5)):790-801 doi:10.1093/infdis/jix605.

    PMID: 29186456
  7. 7

    Neurological Disorders Associated with Human Alphaherpesviruses.

    Kawada JI

    Advances in experimental medicine and biology 2018; (1045()):85-102 doi:10.1007/978-981-10-7230-7_5.

    PMID: 29896664
  8. 8

    Feasibility of Continuous Infusions of Acyclovir.

    O'Leary CK, Jones C, Bryant PA, et al.

    The Pediatric infectious disease journal 2020; (39(9)):830-832 doi:10.1097/INF.0000000000002692.

    PMID: 32796409
  9. 9

    Herpes Simplex Virus in the Neonate.

    Wang A, Wohrley J, Rosebush J

    Pediatric annals 2017; (46(2)):e42-e46 doi:10.3928/19382359-20170112-01.

    PMID: 28192576
  10. 10

    Neonatal Herpes Simplex Virus Infection: Epidemiology and Outcomes in the Modern Era.

    Melvin AJ, Mohan KM, Vora SB, et al.

    Journal of the Pediatric Infectious Diseases Society 2022; (11(3)):94-101 doi:10.1093/jpids/piab105.

    PMID: 34894240
  11. 11

    Neonatal herpes simplex presenting as a zosteriform eruption.

    Anderson E, Johns E, Conlon J, Saleh E

    BMJ case reports 2023; (16(1)) doi:10.1136/bcr-2022-252627.

    PMID: 36657819
  12. 12

    Acyclovir-Induced Nephrotoxicity in Adults with Viral Encephalitis.

    Batool R, Zehra SN

    Journal of the College of Physicians and Surgeons--Pakistan : JCPSP 2024; (34(2)):151-155 doi:10.29271/jcpsp.2024.02.151.

    PMID: 38342863
  13. 13

    Interdisciplinary Systems-Based Intervention to Improve IV Hydration during Parenteral Administration of Acyclovir.

    Dubrofsky L, Kerzner RS, Delaunay C, et al.

    The Canadian journal of hospital pharmacy 2016; (69(1)):7-13 doi:10.4212/cjhp.v69i1.1517.

    PMID: 26985083
  14. 14

    Safety of High-dose Acyclovir in Infants With Suspected and Confirmed Neonatal Herpes Simplex Virus Infections.

    Ericson JE, Gostelow M, Autmizguine J, et al.

    The Pediatric infectious disease journal 2017; (36(4)):369-373 doi:10.1097/INF.0000000000001451.

    PMID: 27977557
  15. 15

    Acyclovir extravasation in a newborn: a case report.

    Shamel S, Zarkesh MR

    Journal of medical case reports 2024; (18(1)):271 doi:10.1186/s13256-024-04585-1.

    PMID: 38845030

This page explains IV acyclovir treatment for neonatal HSV for educational purposes. Always consult your NICU team and pediatric infectious disease specialists about your baby's specific medication protocol and care plan.

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