A herpes antiviral (prodrug of aciclovir)
Valaciclovir
An antiviral for herpes infections, including cold sores, genital herpes and shingles.
What is Valaciclovir?
Valaciclovir is an antiviral medicine used to treat and help prevent herpes infections, such as cold sores, genital herpes and shingles. It works best when started as early as possible in an outbreak. It is taken as a tablet, with plenty of fluids, for the course your prescriber recommends.
Education and reference only. This is a plain-language guide to Valaciclovir — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Valaciclovir is an antiviral medicine used for infections caused by the herpes family of viruses — including cold sores, genital herpes and shingles (and chickenpox in some cases). It is a 'prodrug' of aciclovir, meaning the body converts it into aciclovir after it is taken; this makes it better absorbed and means it can usually be taken fewer times a day than plain aciclovir. It is used both to treat outbreaks and, in some people, to reduce how often they happen.
How it works
Once taken, valaciclovir is converted in the body into aciclovir. Aciclovir is taken up mainly by virus-infected cells and then blocks the enzyme the herpes virus uses to copy its DNA. This stops the virus multiplying, so the outbreak settles faster. It does not remove the virus from the body, which is why outbreaks can recur and why prompt treatment matters.
Practical use
How to take Valaciclovir
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Start the course as early as possible in an outbreak, at the first tingling or warning signs.
- Take the tablets with water at evenly spaced times, with or without food.
- Drink plenty of fluids throughout the course to keep well hydrated.
- Complete the full course as directed, even if symptoms improve.
- Tell your prescriber about any kidney problems, as the amount may need adjusting.
Weighing it up
Advantages & disadvantages of Valaciclovir
Advantages
- Better absorbed than plain aciclovir, so it can usually be taken fewer times a day.
- Effective for cold sores, genital herpes and shingles, and to help prevent frequent recurrences.
- Taken as a convenient oral tablet at home.
Disadvantages
- Works best only if started very early in an outbreak.
- Does not cure the infection — the virus stays in the body and outbreaks can return.
- Needs good hydration and may require a lower amount if the kidneys are impaired.
Practical use
Good to know
It works best when started at the very first signs of an outbreak — such as tingling or itching before a cold sore appears — rather than once it is fully developed. Drink plenty of fluids while taking it to protect the kidneys, especially at higher courses such as for shingles. People with reduced kidney function may need a lower amount, so tell your prescriber about any kidney problems.
Who should not take it / use with caution
- People who have had a serious reaction to valaciclovir or aciclovir.
- Used with caution and at an adjusted level in those with reduced kidney function or who are dehydrated.
- Caution in older or frail people, who are more prone to confusion and dehydration — extra fluids are encouraged.
Monitoring
- Hydration, especially with higher courses such as for shingles
- Kidney function in those at risk
- For any confusion or unusual drowsiness
Side effects
- Headache, nausea, or stomach upset.
- Dizziness or tiredness.
- Rarely, confusion or hallucinations (more likely with kidney problems or dehydration), or kidney effects — report these and keep well hydrated.
Key interactions
- Other medicines that can affect the kidneys may add to the risk — tell your prescriber about them.
- Care alongside some medicines cleared by the kidney, such as certain immune-suppressing drugs.
- Generally few interactions, but check new medicines with your pharmacist.
Available as: Tablets.
Answers
Valaciclovir: frequently asked questions
When should I start taking valaciclovir for a cold sore or outbreak?
As early as possible — ideally at the first tingling, itching or warning signs, before blisters fully appear. Starting promptly gives the best chance of shortening the outbreak; once it is well established, the benefit is smaller.
Does valaciclovir cure herpes?
No. It treats and helps prevent outbreaks, but the virus stays in the body, so outbreaks can still recur. For people who get frequent recurrences, it can be taken regularly to make them less common.
Why do I need to drink plenty of fluids?
Staying well hydrated helps protect your kidneys, which clear the medicine from the body. This is especially important at higher courses, such as for shingles, and in older people.
How is valaciclovir different from aciclovir?
Valaciclovir is converted into aciclovir in the body, but it is absorbed better. This usually means it can be taken fewer times a day than plain aciclovir for the same effect.
Is Valtrex the same as valaciclovir?
Yes. Valaciclovir is the active-ingredient (generic) name and Valtrex is a brand name; they contain the same antiviral medicine.
The wider class
About Herpes antivirals
Valaciclovir belongs to the herpes antivirals class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF: Valaciclovir.
- NICE CKS: Valaciclovir.
- electronic Medicines Compendium (SmPC): Valaciclovir (Valtrex).
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