Disclaimer: This article is for informational purposes only and does not constitute medical advice. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a physician or other qualified health provider with any questions you may have regarding a medical condition.
Overview
Valacyclovir is a prescription antiviral medicine used to treat infections caused by herpes viruses: cold sores (herpes labialis), genital herpes and shingles (herpes zoster). Valtrex is the original brand, and generic valacyclovir tablets are also sold in Canada in 500 mg and 1000 mg strengths.
Valacyclovir does not remove the virus from the body, so it does not cure herpes. It slows the virus from multiplying, which can shorten an outbreak, ease pain and reduce viral shedding. Taken every day, it can also lower the number of genital herpes outbreaks and, together with safer sex practices, reduce the risk of passing genital herpes to a partner.
Because it works best when started early, it helps to have a plan before the next outbreak. BC residents can speak with a BC-licensed doctor by phone through Avee Health about their symptoms and whether a prescription is appropriate.
In Canada, valacyclovir is authorized for:
- Treatment of cold sores (herpes labialis) in adults and teens 12 years and older
- Treatment of a first episode and of recurrent episodes of genital herpes in adults
- Daily suppressive therapy to prevent recurrent genital herpes outbreaks in adults
- Reducing the risk of passing genital herpes to a partner, when used daily with safer sex practices
- Treatment of shingles (herpes zoster) in adults
Health Canada has not authorized valacyclovir for children under 12. Its safety and effectiveness have not been established for most people with a weakened immune system, apart from suppression of genital herpes in adults living with HIV.
Valacyclovir
Antiviral (nucleoside analogue, prodrug of acyclovir)
other
Prescription required
Available
How Valacyclovir Works
Valacyclovir is a prodrug: after it is swallowed, the body quickly converts almost all of it into acyclovir, the active antiviral. Valacyclovir is absorbed better than acyclovir tablets, which is why it can be taken less often.
Inside cells infected with a herpes virus, a viral enzyme activates acyclovir. The activated form blocks the enzyme the virus uses to copy its DNA, so the virus cannot multiply. Healthy, uninfected cells activate very little of the medicine.
It has no effect on the virus while it lies dormant in nerve cells. That is why outbreaks can return after treatment, and why the medicine works best when started at the very first symptoms, while the virus is actively multiplying.
Dosage Instructions of Valacyclovir
Take valacyclovir exactly as your prescriber directs. The dose depends on the condition being treated. The Canadian Valtrex product monograph gives these usual adult doses:
- Cold sores: 2000 mg twice in one day, with the second dose about 12 hours after the first (and not less than 6 hours). Start at the first tingle, itch or burning. Do not continue past 1 day.
- First episode of genital herpes: 1000 mg twice a day for 10 days
- Recurrent genital herpes: 500 mg twice a day for 3 days, started at the earliest warning sign
- Daily suppression of genital herpes: 1000 mg once a day, or 500 mg once a day for people with 9 or fewer outbreaks a year
- Shingles: 1000 mg three times a day for 7 days, started within 72 hours of the rash appearing
Swallow the tablets whole with water, with or without food, and drink enough fluids during treatment. People with reduced kidney function, including many older adults, need a lower dose, which the prescriber will set.
Missed dose: take it as soon as you remember, unless it is nearly time for the next dose. In that case, skip the missed dose. Do not take a double dose.
Storage Instructions
Store at room temperature, between 15°C and 30°C, protected from light. Keep out of the reach and sight of children.
Side Effects of Valacyclovir
The most common side effects are headache and nausea. In two cold sore trials using the one-day treatment, compared with placebo:
- Headache: 9%, compared with 5%
- Nausea: 4%, compared with 5%
- Diarrhea: 3%, compared with 3%
Vomiting, stomach pain and dizziness can also occur. These effects are usually mild and rarely lead people to stop treatment.
Stop taking valacyclovir and get medical help right away if you have:
- Confusion, agitation, hallucinations, tremor, trouble speaking, seizures or reduced alertness (more likely in older adults and people with kidney problems)
- A widespread rash with blisters or peeling skin, or a rash with fever and swollen glands
- Pain in the side or lower back, or passing much less urine, which can be signs of kidney problems
- Unusual bruising or bleeding, or bloody diarrhea with tiredness and swelling
- Swelling of the face or mouth, hives, or trouble breathing
Important Safety Information About Valacyclovir
- Allergy: do not take valacyclovir if you are allergic to valacyclovir, acyclovir or any ingredient, or if you have had a severe skin reaction to either medicine.
- Kidneys and age: tell your prescriber if you have kidney problems or are 65 or older. Doses that are too high for kidney function have caused kidney failure and nervous system effects.
- Fluids: kidney problems have occurred in people who were not drinking enough. Stay well hydrated during treatment.
- Weakened immune system: tell your prescriber if you have HIV, a transplant or another condition that weakens your immune system.
- Pregnancy and breastfeeding: talk to your prescriber first. Acyclovir passes into breast milk.
- Genital herpes is still contagious: valacyclovir alone does not prevent transmission. Herpes can spread without visible sores, so use condoms and avoid sexual contact during outbreaks or warning signs.
- Driving: see how the medicine affects you before driving or using machinery.
Drug Interactions
No clinically significant interactions have been identified at usual doses. Tell your prescriber and pharmacist about everything you take, including vitamins and natural products. Points to know:
- Cimetidine and probenecid raise acyclovir levels in the blood. No dose change is usually needed at standard doses.
- Medicines that can affect the kidneys, such as cyclosporine or tacrolimus: kidney function may need monitoring, especially at higher valacyclovir doses.
- Food does not affect how valacyclovir works.
Brands & DIN Number of Valacyclovir
Brand Names
Valtrex
Key Takeaways
- 1Valacyclovir (Valtrex) is a prescription antiviral used for cold sores, genital herpes and shingles.
- 2It does not cure herpes. It helps outbreaks heal faster and, taken daily, can reduce how often they come back.
- 3Timing matters: it works best when started at the first tingle, itch or burning, or as soon as possible after a shingles rash appears.
- 4For cold sores, treatment is one day only: two doses about 12 hours apart.
- 5Drink enough fluids while taking it. People with kidney problems and older adults may need a lower dose.
- 6Stop and get medical help right away for confusion, hallucinations, a severe skin rash or signs of an allergic reaction.
Frequently Asked Questions
Do I need a prescription for valacyclovir in Canada, and how do I get it in BC?
How fast does valacyclovir work on a cold sore?
Does valacyclovir cure herpes?
Can valacyclovir stop me from passing genital herpes to my partner?
What is the difference between valacyclovir and acyclovir?
Can I drink alcohol while taking valacyclovir?
How much does valacyclovir cost in Canada?
When should I see a doctor about a cold sore, genital sores or shingles?
Avee Editorial
Avee Editorial Team