Zovirax Tablets 400 mg aciclovir – patient leaflet, side effects, dosage

1 What Zovirax is and what it is used for

Zovirax Tablets 400 mg (called ‘Zovirax’ in this leaflet) contains a medicine called aciclovir. This belongs to a group of medicines called antivirals. It works by killing or stopping the growth of viruses.

Zovirax can be used to:

• treat chickenpox and shingles
• treat cold sores, genital herpes and other herpes simplex infections.
• stop these problems returning after you have had them
• stop these problems in people whose immune systems work less well, which means their bodies are less able to fight infections.

2 What you need to know before you take Zovirax

Do not use Zovirax:

• if you are allergic to aciclovir or valaciclovir or any of the other ingredients of this medicine (listed in

  Section 6).

Do not take Zovirax if the above applies to you. If you are not sure, talk to your doctor or pharmacist before taking Zovirax.

Warnings and precautions

Talk to your doctor or pharmacist before taking Zovirax if:

• if you have had severe skin reactions with Zovirax or valaciclovir
• you have kidney problems
• you are over 65 years of age.

If you are not sure if the above apply to you, talk to your doctor or pharmacist before taking Zovirax. It is important that you drink plenty of water while taking Zovirax

Conditions you need to look out for

Zovirax can cause severe skin reactions. You must look out for certain symptoms while you are taking Zovirax, to reduce the risk of any problems. If you experience any signs or symptoms of severe skin reactions, stop using Zovirax and contact your doctor immediately (see ‘Possible side effects’).

Other medicines and Zovirax

Tell your doctor or pharmacist if you are taking, have recently taken or might take any other medicines. This includes medicines obtained without a prescription, including herbal medicines.

In particular tell your doctor or pharmacist if you are taking any of the following medicines:

• probenecid, used to treat gout
• cimetidine, used to treat stomach ulcers
• mycophenolate mofetil, used to stop your body rejecting transplanted organs.

Pregnancy, breast-feeding and fertility

If you are pregnant or breast-feeding, think you may be pregnant or are planning to have a baby, ask your doctor or pharmacist for advice before using any medicine.

Driving and using machines

Some side effects such as feeling drowsy or sleepy may impair your ability to concentrate and react. Make sure you are not affected before you drive or operate machinery.

Important information about the contents of Zovirax Tablets

This medicine contains less than 1mmol sodium (23 mg) per dosage unit, that is to say essentially ‘sodium-free’.

3 How to take Zovirax

Always take this medicine exactly as your doctor has told you. Check with your doctor or pharmacist if you are not sure.

Taking this medicine

• Take this medicine by mouth.
• Dissolve the tablet in a glass of water and stir before drinking.
• If you prefer, the tablet can also be swallowed whole with a little water.
• Start to take Zovirax as soon as possible.

The dose that you should take will depend on what you have been given Zovirax for. Your doctor will discuss this with you. 200 mg and 800 mg tablets are also available.

Treatment of chickenpox and shingles

• The usual dose is two 400 mg tablets taken five times a day.

• You should space each dose by 4 hours.

  Suggested times are: 7am, 11am, 3pm, 7pm and 11pm.

• You should take Zovirax for seven days.

Treatment of cold sores and genital herpes

• The usual dose is 200 mg taken five times a day.

• You should space each dose by 4 hours.

  Suggested times are: 7am, 11am, 3pm, 7pm and 11pm.

• You should take Zovirax for five days, or longer if your doctor tells you to. Stopping these problems returning after you have had them
• The usual dose is 200 mg taken four times a day.
• You should try to space each dose by 6 hours.
• You should take Zovirax until your doctor tells you to stop.

Stopping these problems in people whose immune systems work less well and whose bodies are less able to fight infections

• The usual dose is 200 mg taken four times a day.
• You should try to space each dose by 6 hours.
• You should take Zovirax until your doctor tells you to stop.

Your doctor may adjust the dose of Zovirax if:

• it is for a child
• you are over 65 years of age
• you have kidney problems. If you have kidney problems, it is important to drink plenty of water while you are being treated with Zovirax.

Talk to your doctor before taking Zovirax if any of the above apply.

If you take more Zovirax than you should

Zovirax is not usually harmful, unless you take too much over several days. Talk to your doctor or pharmacist if you take too much Zovirax. Take the medicine pack with you.

If you forget to take Zovirax

• If you forget to take Zovirax, take it as soon as you remember. However, if it is nearly time for your next dose, skip the missed dose.
• Do not take a double dose to make up for a forgotten dose.

4 Possible side effects

Like all medicines, this medicine can cause side effects, although not everybody gets them. The following side effects may happen with this medicine:

Conditions you need to look out for

Allergic reactions (may affect up to 1 in 1,000 people)

If you have an allergic reaction, stop taking Zovirax and see a doctor straight away. The signs may include:

• rash, itching or hives on your skin
• swelling of your face, lips, tongue or other parts of your body
• shortness of breath, wheezing or trouble breathing
• collapse

Severe skin reactions: These are very rare (these may affect up to 1 in 10,000 people) taking Zovirax. Signs include:

• widespread red or scaly rash with blisters (that may contain pus), bumps under the skin or peeling of skin. Flu-like symptoms with a rash, fever, swollen glands, and abnormal blood test results.

➔ Contact a doctor immediately if you get these symptoms. Stop taking Zovirax.

Other side effects include:

Common (may affect up to 1 in 10 people)

• headache
• feeling dizzy
• feeling or being sick
• diarrhoea
• stomach pains
• rash
• skin reaction after exposure to light (photosensitivity)
• itching
• feeling tired
• unexplained fever (high temperature) and feeling faint, especially when standing up.

Uncommon (may affect up to 1 in 100 people)

• itchy, hive-like rash
• hair loss.

Rare (may affect up to 1 in 1,000 people)

• effects on some blood and urine tests
• increases in the enzymes that work in the liver.

Very rare (may affect up to 1 in 10,000 people)

• reduced numbers of red blood cells (anaemia)
• reduced numbers of white blood cells (leukopenia)
• reduced numbers of blood platelets (cells that help blood to clot) (thrombocytopenia)
• feeling weak
• feeling agitated or confused
• shaking or tremors
• hallucinations (seeing or hearing things that aren’t there)
• fits
• feeling unusually sleepy or drowsy
• unsteadiness when walking and lack of coordination
• difficulty speaking
• inability to think or judge clearly
• unconsciousness (coma)
• paralysis of part or all of your body
• disturbances of behaviour, speech and eye movements
• stiff neck and sensitivity to light
• inflammation of the liver (hepatitis)
• yellowing of your skin and whites of your eyes (jaundice)
• kidney problems where you pass little or no urine
• pain in your lower back, the kidney area of your back or just above your hip (renal pain)
• severe skin reactions, such as widespread red or scaly rash with blisters (that may contain pus), bumps under the skin or peeling of skin. Flu-like symptoms with a rash, fever, swollen glands, and abnormal blood test results. (see ‘Conditions you need to look out for’).

Reporting of side effects

If you get any side effects, talk to your doctor or pharmacist. This includes any possible side effects not listed in this leaflet.

You can also report side effects directly via the Yellow Card Scheme at: www.mhra.gov.uk/yellowcard or search for MHRA Yellow Card in the Google Play or Apple App Store. By reporting side effects you can help provide more information on the safety of this medicine.

5 How to store Zovirax

• Keep this medicine out of the sight and reach of children.
• Do not store above 30°C.
• Store in the original package.
• Do not use this medicine after the expiry date which is stated on the carton after Exp. The expiry date refers to the last day of that month.
• Do not throw away any medicines via wastewater or household waste. Ask your pharmacist how to throw away medicines you no longer use. These measures will help protect the environment.

6 Contents of the pack and other information

What Zovirax Tablets 400 mg contain

• The active substance is aciclovir.
• The other ingredients are microcrystalline cellulose, aluminium magnesium silicate, sodium starch glycollate, povidone K30, magnesium stearate, iron oxide, red E172, purified water, industrial methylated spirit, ethanol, hypromellose, polyethylene glycol 400, titanium dioxide, polyethylene glycol 8000.

What Zovirax looks like and contents of the pack

Zovirax Tablets 400 mg are supplied to you in child resistant blister packs enclosed in a carton. Available in packs of 25 or 56 tablets. They are white, shield-shaped tablets marked “GXCF5” on one side.

Not all pack sizes may be marketed.

Each 400 mg tablet contains 400 mg aciclovir.

Marketing authorisation holder and manufacturer

Marketing authorisation holder

The Wellcome Foundation Ltd, 79 New Oxford Street, London, WC1A 1DG, United Kingdom

Manufacturer

Glaxo Wellcome S.A., Aranda de Duero, Burgos, Spain

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Product name Zovirax Tablets 400 mg

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This leaflet was last revised in September 2025.

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