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[Pharmacology](https://durgical.com/en/pharmacology/) · [Anti-herpesvirus agents](https://durgical.com/en/pharmacology/classes/anti-herpesvirus-agents/)

# Valaciclovir

An oral prodrug that the body turns into aciclovir. It is much better absorbed, so it is taken less often for herpes and shingles.

Updated 2026-11-01

- Class: [Anti-herpesvirus agents](https://durgical.com/en/pharmacology/classes/anti-herpesvirus-agents/)
- Enzyme: Viral DNA polymerase (through its active form, aciclovir)
- ATC code: J05AB11
- WHO Model List of Essential Medicines

Also called: valacyclovir

✂**Viral DNA polymerase (through its active form, aciclovir)**Valaciclovir

ⓘ The figure shows aciclovir triphosphate, the active form made from valaciclovir, in the herpes simplex virus 1 DNA polymerase bound to DNA (cryo-EM).

**Target in 3D:** Viral DNA polymerase (through its active form, aciclovir). PDB structure 8V1T (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/8V1T) · Drag to rotate · pinch to zoom

## Mechanism of action

Valaciclovir is the L-valyl ester of aciclovir. After absorption it is converted rapidly and almost completely into aciclovir and valine. From then on it acts like aciclovir: the viral thymidine kinase starts its activation, and aciclovir triphosphate inhibits the viral DNA polymerase and ends the DNA chain.

- Absorbed in the gut and converted to aciclovir
- Viral thymidine kinase phosphorylates aciclovir in infected cells
- Aciclovir triphosphate inhibits the viral DNA polymerase
- Viral DNA synthesis stops

## Pharmacokinetics

**Absorption**
Well absorbed by mouth; aciclovir bioavailability about 55%, several times that of oral aciclovir

**Metabolism**
Converted to aciclovir and valine in the gut wall and liver

**Elimination**
As aciclovir, mainly in the urine

**Half-life**
Aciclovir about 2.5 to 3.3 hours with normal kidney function

## Indications

- Cold sores (herpes labialis)
- Genital herpes: first episode, recurrences, suppressive therapy and reducing transmission to a partner [Genital herpes (herpes simplex infection) →](https://durgical.com/en/conditions/genital-herpes/)
- Herpes zoster (shingles) in adults [Herpes zoster (shingles) →](https://durgical.com/en/conditions/herpes-zoster/)
- Chickenpox in children [Varicella (chickenpox) →](https://durgical.com/en/conditions/varicella/)

## Adverse effects

### Common

- Headache
- Nausea
- Abdominal pain

### Serious (rare, important)

- Acute kidney injury
- Central nervous system effects (agitation, hallucinations, confusion, seizures), more in older people and in kidney disease
- Thrombotic thrombocytopenic purpura/haemolytic uraemic syndrome
- Severe skin reactions

## Contraindications

- Hypersensitivity to valaciclovir, aciclovir or any component, including severe skin reactions

## Key interactions

**Other drugs**
The label lists no clinically significant drug or food interactions; kidney function and hydration matter more

## What is monitored

- Kidney function in older people and in kidney disease
- Mental status in older people

## Administration and safety

- Oral
- Started as early as possible in an outbreak (ideally at the first symptoms)
- Look-alike/sound-alike risk with valganciclovir, a different drug with serious toxicity

## Nursing care

- Ask about kidney disease and age before starting
- Encourage fluids
- Teach to report confusion, hallucinations or reduced urine
- Explain that suppressive therapy lowers but does not remove the risk of passing on genital herpes; condoms and avoiding contact during outbreaks still matter

## Pregnancy and breastfeeding

Decades of data have not shown a drug-related increase in major birth defects; untreated herpes in pregnancy carries risks to the baby.

## Memory aid

VAL-aciclovir = aciclovir with a VALine «backpack» that carries it through the gut wall.

## Test yourself

Think of the answer, then tap the question to see it.

## What is valaciclovir converted into after absorption?

Aciclovir (and the amino acid valine).

## What is the advantage of valaciclovir over oral aciclovir?

Much better absorption, so higher aciclovir levels with fewer doses a day.

## Which patients are at higher risk of confusion or hallucinations with valaciclovir?

Older people and people with kidney disease.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/valaciclovir/)

## Related drugs

- [Aciclovir](https://durgical.com/en/pharmacology/aciclovir/)
- [Famciclovir](https://durgical.com/en/pharmacology/famciclovir/)

## Related conditions

- [Genital herpes (herpes simplex infection)](https://durgical.com/en/conditions/genital-herpes/)
- [Herpes zoster (shingles)](https://durgical.com/en/conditions/herpes-zoster/)
- [Varicella (chickenpox)](https://durgical.com/en/conditions/varicella/)

[← Back to the class: Anti-herpesvirus agents](https://durgical.com/en/pharmacology/classes/anti-herpesvirus-agents/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [DailyMed - VALACYCLOVIR HYDROCHLORIDE tablet, film coated](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f5cfb61e-d971-4a9c-b9ef-4f3368fe02f5) (DailyMed (U.S. National Library of Medicine), 2026); [Herpes simplex virus](https://www.who.int/news-room/fact-sheets/detail/herpes-simplex-virus) (World Health Organization, 2025); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=J05AB11) (WHO Collaborating Centre for Drug Statistics Methodology, 2026); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/) (World Health Organization, 2025).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/valaciclovir/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/valaciclovir/