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Tablets for cold sores

Written by Healthwords's team of doctors and pharmacists based in UK | Updated: 26.01.2023 | 2 min read

Aciclovir and valaciclovir tablets are prescription-only antiviral medicines used occasionally to treat persistent cold sores. They do not cure a cold sore (Herpes Simplex virus) infection but help to reduce the severity and length of the outbreak. In people with frequent outbreaks and in those who have a weak immune system, aciclovir and valaciclovir tablets can be used to help reduce the number of future outbreaks as preventative medication.

Who is it for?

When treating cold sores with aciclovir or valaciclovir tablets, you should take your prescribed dose as soon as you recognise the tingling or burning sensation at the site of the outbreak, ideally within 5 days. Cold sores are an infection caused by the herpes simplex virus – once you’ve had contact with the virus, it lies dormant in the nerves of the skin and may flare up from time to time. You might recognise triggers – stress and exposure to the cold or sun are common ones.

How does it work?

Aciclovir and Valaciclovir are antiviral agents that interfere with the growth and replication of viral particles, helping your immune system to target and tackle the virus. In the body, valaciclovir is metabolised into aciclovir.

Prescribed treatments are best to be used in the initial stages of an outbreak, usually within the first 5 days. For treatment of outbreaks, you will be taking a high dose for a short course, usually for 5 days. If you have a weakened immune system, treatment doses are usually double the standard doses for healthy individuals. Suppressive antiviral treatment is an option for frequent (usually 6 or more through the year) cold sore outbreaks causing distress or if outbreaks are affecting your social life. Doses vary depending on your age and kidney function. In healthy adults, treatment of your first outbreak with aciclovir tablets involves a course of 200mg five times per day for five days or 500mg twice a day for 5 days with valaciclovir tablets.

Should anyone avoid taking it?

Do not take aciclovir or valaciclovir tablets if you have previously experienced an allergic reaction to aciclovir or any ingredients used to make aciclovir tablets.

Are there any side-effects?

Aciclovir and valaciclovir are generally well tolerated in most individuals. A small number of patients may experience symptoms of fatigue, headache, feeling dizzy, nausea, vomiting, abdominal pain, itching and a rash (including sensitivity to light).

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