Zovirax is used to treat viral infections such as genital herpes (a sexually transmitted infection), cold sores, shingles (sometimes called herpes zoster), and chickenpox. Shingles and chickenpox are caused by the varicella-zoster virus.

How does Zovirax work?

  • Zovirax dispersible tablets and Zovirax suspension both contain the active ingredient aciclovir, which is an antiviral medicine used to treat infections with herpes viruses. (NB. Aciclovir is also available without a brand name, ie as the generic medicine.)
  • The herpes viruses include the viruses that cause cold sores and genital herpes (herpes simplex 1 and 2) and the virus that causes chickenpox and shingles (varicella zoster or herpes varicellae).
Aciclovir works by stopping these herpes viruses from reproducing and infecting more cells in the body.
  • Zovirax is converted to a more active form inside cells of the body that are infected with herpes viruses. The activated aciclovir then works by blocking the action of a viral enzyme called DNA polymerase.
  • The herpes viruses need the DNA polymerase enzyme to copy their genetic material from RNA to DNA. This process is necessary for the viruses to multiply and continue to survive. By blocking the action of DNA polymerase, aciclovir prevents the herpes viruses from multiplying. This controls the infection and helps the immune system to deal with it.
  • Zovirax is taken by mouth to treat herpes infections that cause chickenpox and shingles. It is also taken by mouth to treat genital herpes and other herpes simplex infections of the skin and mucous membranes, and to prevent these infections coming back in people who suffer recurrent infections. Oral zovirax is also valuable for preventing herpes simplex infections in people whose immune systems are supressed and cannot fight off infection, either due to disease, eg HIV and AIDS, or medical treatment, eg chemotherapy, steroids, bone marrow transplant.
  • Zovirax is also available as creams specifically for treating genital herpes and cold sores, and as an eye ointment for treating herpes simplex infections of the eye. 
  • Before taking Zovirax

    Before taking zovirax make sure your doctor or pharmacist knows:

    • If you are pregnant, trying for a baby or breast-feeding.
    • If you have kidney problems.
    • If you are over 65 years of age.
    • If you are taking other medicines, including those available to buy without a prescription, herbal or complementary medicines.
    • If you have ever had an allergic reaction to this or to any other medicine.

    How to take Zovirax

    • Before beginning treatment, read the manufacturer's printed information leaflet.
    • Take zovirax exactly as directed by your doctor. It can be taken before or after food.
    • Try to take zovirax at the same times each day to avoid missing any doses. Spread your doses out evenly during the day.
    • If you have been prescribed the dispersible tablet form of zovirax they should be dissolved in a glass of water.
    • You must complete the course of zovirax, otherwise your infection may return.
    • If you forget to take a dose, take it as soon as you remember unless it is nearly time for your next dose, in which case leave out the missed dose. Do not take two doses together to make up for a missed dose.

    What is Zovirax used for?

    Not to be used in

    This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.

    If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

    Pregnancy and breastfeeding

    • Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.
    • This medicine should be used with caution during pregnancy, and only if the expected benefit to the mother is greater than any possible risk to the developing baby. Seek medical advice from your doctor.
    • This medicine passes into breast milk. It should be used with caution by breastfeeding mothers and only if the expected benefit to the mother is greater than any possible risk to the nursing infant. Seek medical advice from your doctor.

    Side effects

    Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Just because a side effect is stated here, it does not mean that all people using this medicine will experience that or any side effect.

    Common (affect between 1 in 10 and 1 in 100 people)

    Rare (affect between 1 in 1000 and 1 in 10,000 people)

    Very rare (affect less than 1 in 10,000 people)

    • Decrease in the number of white blood cells (leukopenia), red blood cells (anaemia) or platelets (thrombocytopenia) in the blood.
    • Confusion.
    • Agitation.
    • Tremor.
    • Shaky movements and unsteady walk (ataxia).
    • Speech problems.
    • Convulsions.
    • Sleepiness.
    • False perceptions of things that are not really there (hallucinations).
    • Psychotic symptoms.
    • Yellowing of the skin and whites of the eyes (jaundice).
    • Inflammation of the liver (hepatitis).
    • Kidney pain.
    • Kidney failure.

    The side effects listed above may not include all of the side effects reported by the medicine's manufacturer. For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

    How can Zovirax affect other medicines?

    It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while taking this one, to make sure that the combination is safe.

    There may possibly be an increased risk of side effects on the kidneys if zovirax is used in combination with the following medicines, and your doctor may want to monitor your kidney function if you are taking aciclovir with either of these:

    • ciclosporin
    • tacrolimus.

    The following medicines may decrease the removal of zovirax from the body by the kidneys, but this does not usually require any dose adjustments:

    • cimetidine
    • mycophenolate
    • probenecid.

    How to store Zovirax

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

    If you have any more questions please ask your Pharmacist.

    Remember to keep all medicines out of reach of children

    Please Note: We have made every effort to ensure that the content of this information sheet is correct at time of publish, but remember that information about drugs may change. This sheet does not list all the uses and side-effects associated with this drug. For full details please see the drug information leaflet which comes with your medicine. Your doctor will assess your medical circumstances and draw your attention to any information or side-effects which may be relevant in your particular case.