A herpes antiviral
Famciclovir
An antiviral medicine for herpes infections such as shingles (herpes zoster) and genital herpes, and sometimes recurrent cold sores; it works best when started as early as possible.
What is Famciclovir?
Famciclovir is an antiviral medicine used to treat infections caused by the herpes family of viruses, mainly shingles (herpes zoster) and genital herpes, and sometimes recurrent cold sores. It works by stopping the virus from copying itself, which shortens an attack and eases symptoms. It is most effective when started as early as possible, ideally at the very first signs of an outbreak.
Education and reference only. This is a plain-language guide to Famciclovir — 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
Famciclovir is an antiviral medicine used in the UK to treat infections caused by herpes viruses, mainly shingles (herpes zoster) and genital herpes (both first attacks and recurrences, and sometimes to suppress frequent ones), and occasionally recurrent cold sores. After it is swallowed, the body converts it into its active form (penciclovir), which acts on the virus. It does not cure or remove the virus, which stays dormant in the body, but it controls outbreaks, shortens how long they last and reduces symptoms when used at the right time.
How it works
Herpes viruses cause illness by getting inside the body's cells and copying their genetic material to make more virus. Famciclovir is turned into its active form, which the virus's own enzymes then activate further inside infected cells. This active form blocks the viral enzyme needed to copy the virus's DNA, so the virus cannot multiply. By halting viral copying it limits the spread of the infection, which speeds healing and reduces the severity of an outbreak; because it targets the active virus, it works best when started early.
Company & origin
Originated / developed by: Originally developed by SmithKline Beecham (now part of GSK/Novartis)..
Famciclovir is an antiviral developed in the early 1990s for herpes infections, taken by mouth and converted in the body into its active form, penciclovir.
Practical use
How to take Famciclovir
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Start it as early as possible — at the very first signs of an outbreak, such as tingling, itching or burning — for the best effect.
- Take it as prescribed, spacing the doses evenly, and complete the course even if the outbreak seems to be settling.
- Drink plenty of fluids while taking it to stay well hydrated and support your kidneys.
- It can be taken with or without food.
- Tell your prescriber if you have any kidney problems, as the dose may need adjusting.
- Avoid close skin or sexual contact during an outbreak to reduce the risk of passing the virus on, as the medicine does not prevent transmission entirely.
Weighing it up
Advantages & disadvantages of Famciclovir
Advantages
- It can shorten an outbreak and ease symptoms of cold sores, genital herpes and shingles.
- It is taken by mouth and is generally well tolerated.
- It can also be used to suppress frequent recurrences of genital herpes for some people.
Disadvantages
- It works best only if started very early, so a delay reduces the benefit.
- It controls outbreaks but does not get rid of the virus, so attacks can recur.
- People with reduced kidney function may need a lower dose and extra care.
Practical use
Good to know
Famciclovir works best when started as early as possible — ideally at the very first warning signs of an outbreak, such as the tingling, itching or burning before a cold sore or genital herpes blister appears, or at the first signs of shingles. The earlier it is started, the more it can shorten the attack. It does not get rid of the virus permanently, so further outbreaks can still occur. Drink plenty of fluids while taking it to stay well hydrated, as this helps the kidneys, which clear the medicine. People with reduced kidney function may need extra care, so tell your prescriber about any kidney problems. It can be taken with or without food.
Who should not take it / use with caution
- Anyone who has had a serious allergic reaction to famciclovir or to penciclovir.
- People with significantly reduced kidney function, unless the dose is adjusted and they are monitored.
- Pregnant or breastfeeding women, unless their prescriber considers it necessary.
Monitoring
- Reviewing whether the outbreak is responding to treatment.
- Considering kidney function, particularly in older people or those with kidney problems.
- Watching for any rash or signs of an allergic reaction.
Side effects
- Headache and nausea.
- Dizziness and tiredness.
- Diarrhoea or stomach discomfort.
- Skin rash or itching, and rarely a more serious allergic reaction.
Key interactions
- Other medicines that affect the kidneys may need to be taken into account, so tell your prescriber about all your medicines.
- Probenecid and some other medicines can raise levels of the active drug in the body.
- Generally it has fewer interactions than many medicines, but a full medicines check is still sensible.
Available as: Tablets.
Answers
Famciclovir: frequently asked questions
When should I start famciclovir for a cold sore or herpes outbreak?
As early as possible — ideally at the very first warning signs, such as the tingling, itching or burning before a blister appears. Starting early gives the medicine the best chance to shorten the outbreak and ease symptoms.
Does famciclovir cure herpes?
No. It controls outbreaks by stopping the virus copying itself, which shortens and eases an attack, but it does not remove the virus from the body. The virus stays dormant, so further outbreaks can still happen and treatment may be needed again.
Can I take it for shingles?
Yes. Famciclovir is used to treat shingles, and as with other herpes infections it works best when started at the first signs. Early treatment can reduce the severity of the rash and the pain that goes with it.
Why should I drink plenty of fluids?
Famciclovir's active form is cleared by the kidneys, so staying well hydrated helps protect them. This is especially important if you are older or have any kidney problems, in which case the dose may also need adjusting.
Can I still pass the virus on while taking it?
Yes. The medicine reduces symptoms but does not fully stop the virus being passed to others. Avoid close skin contact or sexual contact during an outbreak, and follow your team's advice on reducing the risk of transmission.
The wider class
About Herpes antivirals
Famciclovir belongs to the herpes antivirals class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF
- NICE CKS
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