Valaciclovir for viral infections (Valtrex)

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You can take valaciclovir tablets before or after food.

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

Drink plenty of water. It is important that you don't get 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 a kidney 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 may 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, trying for a baby, or breast-feeding.
  • If you have any problems with your kidneys or liver.
  • If you are taking or using any other medicines. This includes any medicines you are taking which are available to buy without a prescription, such as herbal and complementary medicines.
  • If you have ever had an allergic reaction to a medicine.
  • Before you start this treatment, read the manufacturer's printed information leaflet from inside your pack. The leaflet will give you more information about valaciclovir and a full list of the side-effects which you may experience from taking it.
  • Your dose will depend upon the type of your infection, 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 be printed on the label of the pack to remind you.
  • Space your doses out evenly during the day. You can take valaciclovir tablets before or after food.
  • Even if you feel your infection has cleared up, keep taking this medicine until the course is finished. A short course of treatment commonly lasts up to seven days. It will be for longer than this if you are taking valaciclovir to prevent further episodes.
  • If you forget to take a dose, take one as soon as you remember. 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 may 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 may reduce this chance.
  • 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 most common ones. You will find a full list in the manufacturer's information leaflet supplied with your medicine. The unwanted effects often improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following continue or become troublesome.

Common valaciclovir side-effectsWhat can I do if I experience this?
HeadacheAsk your pharmacist to recommend a suitable painkiller
Feeling or being sickStick to simple foods - avoid rich or spicy meals
Feeling dizzyIf this happens, do not drive or use tools or machines until you feel better
DiarrhoeaDrink plenty of water to replace any lost fluids
Itchy rashIf this becomes troublesome, speak with your doctor

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

  • 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 make no warranty as to its accuracy. Consult a doctor or other health care 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 (v25)
Last Checked:
Next Review:
The Information Standard - certified member

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