Valaciclovir for viral infections (Valtrex)

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You can take valaciclovir tablets either with or without food.

Space out your doses evenly over the day, and complete the full course of treatment.

Drink plenty of water. It is important that you don't become lacking in fluid in the body (dehydrated).
Type of medicineAn antiviral medicine
Used forTo prevent or treat viral infections in adults and young people
Also calledValtrex®
Available asTablets

Valaciclovir is known as a pro-drug. Once inside your body it is broken down into an active ingredient called aciclovir. It is used to treat infections caused by two common viruses - herpes zoster and herpes simplex. The herpes zoster virus is the cause of shingles. Herpes simplex viruses cause cold sores, and genital herpes. You will have been prescribed valaciclovir to treat (or prevent further episodes of) one of these infections.

Valaciclovir works by preventing viruses from multiplying, and this reduces the severity of the infection and stops it from spreading.

As well as treating infections, valaciclovir is also prescribed to prevent some viral infections from occurring. This is particularly the case in people who have had an organ transplant and are at risk of infection from a virus called cytomegalovirus.

Some medicines are not suitable for people with certain conditions, and sometimes a medicine can only be used if extra care is taken. For these reasons, before you start taking valaciclovir it is important that your doctor knows:

  • If you are pregnant or breast-feeding.
  • If you have any problems with the way your kidneys work.
  • If you are taking or using any other medicines. This includes any medicines you are taking which are available to buy without a prescription, as well as herbal and complementary medicines.
  • If you have ever had an allergic reaction to a medicine.
  • Before you start the treatment, read the manufacturer's printed information leaflet from inside the pack. It will give you more information about valaciclovir, and it will also provide you with a full list of the side-effects which you could experience from taking it.
  • Your dose will depend upon the type of infection you have, so take the tablets exactly as your doctor tells you to. Typically, doses range from 500 mg to 2 g, taken 1-4 times daily. Your doctor or pharmacist will tell you what dose is right for you, and this information will also be printed on the label of the pack to remind you about what the doctor said to you.
  • Space out your doses evenly during the day. Swallow the tablets with a drink of water. You can take valaciclovir tablets either with or without food.
  • Even if you feel your infection has cleared up, keep taking valaciclovir until the course is finished (unless your doctor tells you to stop sooner). A short course of treatment commonly lasts for up to 10 days. You will be prescribed a longer course than this if you are taking it to prevent further episodes of infection, or following an organ transplantation.
  • If you forget to take a dose, take it as soon as you remember and then continue as before. Try to take the correct number of doses each day, but do not take two doses at the same time to make up for a missed dose.
  • You should drink plenty while you are on valaciclovir to keep your kidneys working well. Drinking water is best, but hot drinks and non-alcoholic cold drinks are also suitable.
  • Valaciclovir could cause your skin to become more sensitive to sunlight than it is usually. Avoid strong sunlight and sunbeds, and use a sun cream with a high sun protection factor until you know how your skin reacts.
  • If you have been prescribed valaciclovir for genital herpes, do not have sex while you have sores or blisters. Even after these have healed, there is still a small chance that you may pass on the virus when you have sex - using a condom reduces this risk.
  • If you are having an operation or any other medical treatment, tell the person carrying out the treatment that you are taking valaciclovir.

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains some of the more common ones associated with valaciclovir. The best place to find a full list of the side-effects which can be associated with your medicine, is from the manufacturer's printed information leaflet supplied with the medicine. Alternatively, you can find an example of a manufacturer's information leaflet in the reference section below. Speak with your doctor or pharmacist if any of the following continue or become troublesome.

Very common valaciclovir side-effects (these affect more than 1 in 10 people)What can I do if I experience this?
HeadacheDrink plenty of water and ask your pharmacist to recommend a suitable painkiller. If the headache continues, speak with your doctor
Common valaciclovir side-effects
(these affect less than 1 in 10 people)
What can I do if I experience this?
Feeling sick or being sick (vomiting)Stick to simple foods - avoid fatty or spicy meals
Feeling dizzyDo not drive and do not use tools or machines while affected
DiarrhoeaDrink plenty of water to replace any lost fluids
Itching or skin rashIf troublesome, speak with your doctor

If you experience any other symptoms which you think may be due to the medicine, speak with your doctor or pharmacist for further advice.

  • Keep all medicines out of the reach and sight of children.
  • Store in a cool, dry place, away from direct heat and light. 

Never take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of this medicine, go to the accident and emergency department of your local hospital. Take the container with you, even if it is empty.

This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.

If you buy any medicines, check with a pharmacist that they are suitable to take with your other medicines.

Do not keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.

If you have any questions about this medicine ask your pharmacist.

Further reading & references

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but makes no warranty as to its accuracy. Consult a doctor or other healthcare professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Helen Allen
Current Version:
Peer Reviewer:
Dr Adrian Bonsall
Document ID:
1505 (v26)
Last Checked:
19/12/2016
Next Review:
19/12/2019
The Information Standard - certified member

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