Aciclovir

Aciclovir is an antiviral used against the herpes family of viruses — cold sores, shingles, chickenpox and genital herpes. The single most important thing about it is timing: it stops the virus multiplying, so it does most good when started as early as possible and comparatively little once a rash is well established.

What it is used for

• Cold sores — aciclovir cream, started at the first tingle rather than once the blister has formed
• Shingles — tablets, ideally started within 72 hours of the rash appearing
• Chickenpox — tablets, in adults and in children where there is added risk
• Genital herpes — tablets, for treatment or to reduce recurrences
• Herpes simplex eye infections — eye ointment, always under medical supervision

It is also used to prevent these infections in people whose immune system is weakened.

How to use it

Cream: apply five times a day, roughly every four hours while awake, for five days. Start at the first tingling or itching — that is when it makes the most difference. Wash your hands before and after, and use a cotton bud if you prefer. Do not share it, and do not use it inside the mouth or eyes.

Tablets: take exactly as prescribed, spread evenly through the day, and finish the course even if things improve. Drink plenty of water while taking them, particularly if you have any kidney problems.

Eye ointment: use only as directed by the prescriber, and do not wear contact lenses during treatment.

If you miss a dose, take it when you remember unless the next one is nearly due — in which case skip it. Never double up.

Side effects

The cream and eye ointment rarely cause problems beyond mild stinging or burning where applied, which usually passes quickly.

Tablets more commonly cause headache, dizziness, nausea, diarrhoea, stomach ache, rash, tiredness or sensitivity to sunlight. If they make you dizzy, do not drive until it settles.

Rarely, tablets can cause serious effects. Get help urgently for:

• Swelling of the face, throat or tongue, a raised itchy rash, or difficulty breathing
• Yellowing of the eyes or skin, or unusual tiredness with itchy skin
• Passing little or no urine
• Unusual bruising, or repeated infections

Shingles: the 72-hour window

Antiviral treatment for shingles works best when started within 72 hours of the rash appearing. It reduces the severity and duration of the episode and lowers the chance of lasting nerve pain afterwards.

If you think you have shingles, do not wait to see how it develops — that is the window closing. Come and speak to us or contact your GP the same day.

Pregnancy, breastfeeding and other medicines

Aciclovir can usually be used in pregnancy, but check first. The cream and ointment are generally fine while breastfeeding provided the baby does not come into contact with the treated area; discuss tablets with your prescriber.

Tablets may interact with probenecid, cimetidine and mycophenolate mofetil. Tell your prescriber what else you take, including anything bought over the counter or herbal.

You can eat, drink and take alcohol as normal, but keep your fluid intake up.

Frequently asked questions