- Treatment for cold sores with valaciclovir
- Access valaciclovir following an online medical consultation
- What is valaciclovir?
- What is the active substance in valaciclovir?
- Who is the treatment suitable for?
- What dosage is used?
- How does valaciclovir work?
- How is valaciclovir taken?
- When should valaciclovir not be used?
- What side effects can occur?
- Reporting side effects
- Valaciclovir active substance and excipients
Treatment for cold sores with valaciclovir
Valaciclovir is a prescription-only antiviral medicine used in adults for the treatment of cold sores (herpes labialis) caused by the herpes simplex virus (HSV). It is taken orally and works by reducing the severity and duration of outbreaks. Valaciclovir is a prodrug of aciclovir, meaning it is converted into aciclovir in the body after absorption, achieving higher blood levels with less frequent dosing than standard aciclovir tablets.
Access valaciclovir following an online medical consultation
Start the online consultation and complete the medical questionnaire. A UK-registered prescriber will review your answers and, where appropriate, approve a prescription for valaciclovir.
Important information
DoktorABC UK is a digital health platform that connects patients with independent, UK-registered prescribers. DoktorABC UK does not itself provide medical care, issue prescriptions, or dispense medicines. All clinical decisions are made by the UK-registered prescriber following an individual medical assessment.
What is valaciclovir?
Valaciclovir is an oral antiviral medicine belonging to the nucleoside analogue class. It is a prodrug of aciclovir, which means it is absorbed in the gut and rapidly converted into aciclovir in the body, where it then exerts its antiviral effect. This conversion allows valaciclovir to achieve significantly higher blood levels of aciclovir than standard aciclovir tablets taken at the same dose, and with a simpler dosing schedule.
Valaciclovir does not cure cold sores or eliminate the herpes simplex virus from the body. The virus remains dormant in nerve tissue between outbreaks and can reactivate periodically. However, taken early and correctly, valaciclovir can significantly reduce the duration and discomfort of an outbreak.
What is the active substance in valaciclovir?
The active substance is valaciclovir hydrochloride. After absorption, valaciclovir is rapidly and almost completely converted to aciclovir in the intestinal wall and liver. Aciclovir is then taken up preferentially by cells infected with the herpes simplex virus, where it is converted by a viral enzyme into its active form. This active form inhibits the viral DNA polymerase that the herpes simplex virus needs to replicate, reducing the severity and duration of the outbreak.
Who is the treatment suitable for?
Valaciclovir for cold sores may be considered for adults following a medical assessment. It may be appropriate for:
- Adults experiencing a cold sore outbreak who wish to reduce its severity and duration
- Adults who experience frequent or severe cold sore outbreaks
- Adults who have previously used topical treatments with limited benefit and wish to consider an oral antiviral option
- Adults who recognise the early warning signs of a cold sore and wish to begin treatment promptly
Treatment is not suitable for everyone. A full medical assessment is required before prescribing, and your UK-registered prescriber will determine whether valaciclovir is appropriate for your individual circumstances.
What dosage is used?
The standard adult dose for episodic treatment of cold sores is 2,000 mg (2 g) twice daily for one day only, with the two doses taken approximately 12 hours apart. Treatment should begin at the very first sign of a cold sore, during the prodromal phase when tingling, itching, or burning is felt, before any blistering appears.
Your UK-registered prescriber will confirm the most appropriate dosage for your circumstances, including whether a different dosing schedule may be more appropriate based on your health profile.
Good to know: The one-day dosing schedule for cold sores is shorter than that used for genital herpes or other herpes virus infections. Always follow the dosing instructions provided by your UK-registered prescriber and the patient information leaflet supplied with your medication.
How does valaciclovir work?
After being taken orally, valaciclovir is absorbed through the gut wall and rapidly converted into aciclovir in the liver and intestinal tissue. Aciclovir then circulates in the bloodstream and is taken up preferentially by cells infected with the herpes simplex virus.
Inside infected cells, a viral enzyme converts aciclovir into its active form, which then blocks the DNA polymerase the herpes simplex virus uses to copy its genetic material and produce new viral particles. By inhibiting this process, valaciclovir reduces the number of viral particles produced, limiting the spread of the virus and reducing the severity and duration of the cold sore.
Good to know: Valaciclovir achieves approximately three to five times higher blood levels of aciclovir than an equivalent dose of standard aciclovir tablets. This improved bioavailability allows for less frequent dosing while maintaining effective antiviral activity.
How is valaciclovir taken?
Valaciclovir tablets are taken orally. The following guidance helps ensure the treatment is as effective as possible.
- Take each dose with a full glass of water
- Tablets can be taken with or without food
- Take the two doses approximately 12 hours apart on the same day
- Begin treatment at the earliest possible sign of a cold sore, during the tingling or itching phase, for the best results
- Do not take more than the prescribed dose or extend the course without prescriber guidance
When should valaciclovir not be used?
Valaciclovir should not be used if:
- You have a known allergy to valaciclovir, aciclovir, or any of the other ingredients listed in the patient information leaflet
- You have severe kidney impairment without appropriate dose adjustment under prescriber supervision
Before starting treatment, inform your UK-registered prescriber of your full medical history, any allergies, and all medicines you are currently taking, including over-the-counter medicines and supplements. Dose adjustments may be required for people with kidney impairment or certain other health conditions.
What side effects can occur?
As with all medicines, valaciclovir can cause side effects, although not everyone will experience them.
Common side effects (may affect up to 1 in 10 people):
- Headache
- Nausea
- Dizziness
- Vomiting
- Diarrhoea
- Abdominal discomfort
- Skin rash or itching
Uncommon side effects (may affect up to 1 in 100 people):
- Sensitivity to sunlight
- Raised liver enzymes (usually detected on blood tests)
- Mild kidney function changes
Rare side effects:
- Neurological effects including confusion or agitation, more commonly associated with higher doses or in people with kidney impairment
If you experience a severe allergic reaction, including swelling of the face, lips, tongue or throat, difficulty breathing, or a severe skin reaction, stop taking valaciclovir and seek emergency medical help immediately.
If you notice any side effects, inform your UK-registered prescriber.
Reporting side effects
Suspected side effects can also be reported to the MHRA via the Yellow Card scheme.
Valaciclovir active substance and excipients
Active substance:
Valaciclovir hydrochloride equivalent to valaciclovir 500 mg per tablet.
Other ingredients vary by manufacturer and formulation.
Please refer to the patient information leaflet supplied with your medication for a full list of excipients.
