A cold sore cream (topical antiviral)
Penciclovir
An antiviral cream used to treat cold sores on the lips and around the mouth.
What is Penciclovir?
Penciclovir is an antiviral cream used to treat cold sores (herpes labialis), the small painful blisters on the lips and around the mouth caused by the herpes simplex virus. It works by stopping the virus from multiplying, which can shorten an outbreak and ease symptoms. It works best when started as early as possible, ideally at the first tingle, and is applied frequently during the day. The main side effects are local, such as mild stinging, burning or numbness where it is applied. It treats the cold sore rather than curing the virus, which can come back.
Education and reference only. This is a plain-language guide to Penciclovir — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Penciclovir is an antiviral medicine in the form of a cream, used to treat cold sores — the painful blisters that appear on the lips and around the mouth, caused by the herpes simplex virus. It is applied directly to the affected area rather than taken by mouth. Cold sores tend to recur because the virus stays in the body between outbreaks, and penciclovir is used to treat a flare-up when it happens. It is available both on prescription and to buy from pharmacies in the UK.
How it works
Cold sores are caused by the herpes simplex virus multiplying in the skin around the lips. Penciclovir gets into the infected cells and blocks the machinery the virus needs to copy its genetic material, so it cannot multiply as easily. This helps the outbreak settle sooner and can ease pain and discomfort. Because it acts on the actively multiplying virus, it works best when applied very early in an outbreak, at the first warning signs such as tingling or itching, and is applied often through the day to keep working on the affected area.
Company & origin
Originated / developed by: Generic.
An antiviral cream used in the UK to treat cold sores on the lips and around the mouth caused by the herpes simplex virus.
Practical use
How to take Penciclovir
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Start applying it as early as possible, ideally at the first tingle or itch before a blister forms.
- Apply it frequently during the day, usually every couple of hours while awake, to the affected area.
- Use it for the full course recommended, even if the cold sore starts to improve.
- Wash your hands before and after applying it, and avoid getting it in or near the eyes.
- Do not share the cream, as cold sores are contagious, and avoid kissing or oral contact during an outbreak.
Weighing it up
Advantages & disadvantages of Penciclovir
Advantages
- Applied directly to the cold sore, with little absorbed into the rest of the body.
- Can shorten an outbreak and ease symptoms when started early.
- Available to buy from pharmacies as well as on prescription.
Disadvantages
- Works best only if started very early, at the first warning signs.
- Needs to be applied frequently through the day.
- Treats an outbreak but does not cure the virus, which can come back.
Practical use
Good to know
The single most useful thing to know about penciclovir is timing: it works best when you start it as early as possible, ideally at the very first tingle, itch or feeling that a cold sore is coming, even before any blister appears. It is applied frequently during the day, typically every couple of hours while awake, to the affected area. The side effects are usually local and mild, such as a brief stinging, burning, numbness or tingling where it is applied. It is important to understand that it treats an outbreak rather than curing the virus, which stays in the body and can cause cold sores again. Wash your hands after applying it, avoid getting it in the eyes, and do not share the cream, as cold sores are contagious.
Who should not take it / use with caution
- People who have had a serious allergic reaction to penciclovir or a similar antiviral cream should not use it.
- It is for cold sores on the lips and around the mouth, not for use inside the mouth, in the eyes or on the genitals.
- Seek medical advice for cold sores in people with a weakened immune system, or if sores are severe or do not heal.
Monitoring
- Checking that the cold sore is improving and healing as expected.
- Watching for skin irritation or signs of an allergic reaction.
- Seeking advice if cold sores are frequent, severe or slow to heal.
Side effects
- Mild stinging, burning or a feeling of warmth where it is applied.
- Numbness or tingling of the skin in the treated area.
- Occasionally, mild redness or skin irritation.
- Rarely, an allergic skin reaction, which should be reported.
Key interactions
- Because it is a cream used on the skin, troublesome interactions with other medicines are very unlikely.
- Avoid using other creams on the same spot at the same time unless advised.
- Tell your pharmacist or prescriber about other treatments if you are unsure.
Available as: A cream applied to the skin on and around the lips.
Answers
Penciclovir: frequently asked questions
What is penciclovir used for?
It is an antiviral cream used to treat cold sores (herpes labialis) on the lips and around the mouth, caused by the herpes simplex virus.
When should I start using it?
As early as possible — ideally at the first tingle or itch, even before a blister appears — because it works best when started early in an outbreak.
How often do I apply it?
It is applied frequently during the day, usually every couple of hours while awake, to the affected area for the recommended number of days.
Will it cure my cold sores for good?
No. It treats an outbreak but does not cure the herpes virus, which stays in the body and can cause cold sores again in the future.
Does it sting?
Mild stinging, burning, numbness or tingling where it is applied is the most common effect and usually settles quickly.
The wider class
About Topical antiviral (cold sore cream)
Penciclovir belongs to the topical antiviral (cold sore cream) class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
Browse by body system
Authoritative sources
- BNF
- NICE CKS
Building a medicines information resource?
We create evidence-led, dose-free drug and formulary references for teams.