Valacyclovir vs. Acyclovir: Similarities & Differences
Medically reviewed by Erika Prouty, PharmD
For the treatment of conditions caused by herpes viruses, healthcare providers may turn to valacyclovir or acyclovir, two commonly used, prescription-based antiviral medications.
Valacyclovir and acyclovir work to lessen pain and expedite the healing of sores or blisters in people with chickenpox, shingles (also known as herpes zoster), genital herpes (in adults), and cold sores (also known as herpes labialis).
However, while primarily similar, some significant differences exist between valacyclovir and acyclovir, including dosing guidelines, Food and Drug Administration (FDA)-approved uses, brand-name affiliations, and slightly different side effects.
To explain these similarities and differences and discuss other pertinent information related to their safe and effective use, this article will provide an in-depth comparison of valacyclovir and acyclovir.
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Understanding Herpes Viruses
The virus that most commonly causes cold sores, herpes simplex virus 1 (HSV-1), is a prevalent sexually transmitted infection (STI), that has affected 67% of the world's population. HSV-1 is commonly referred to as oral herpes.
Oral herpes tends to affect your mouth or face and causes cold sores. It spreads through contact with saliva.
In comparison, the other type of herpes, herpes simplex virus 2 (HSV-2), is also highly prevalent.
HSV-2 causes genital herpes, infecting nearly 13% of the world's population. HSV-2 causes sores on the skin following physical contact with the genitals of an infected person. Herpes sores typically last a week to 10 days.
Similar to HSV-1 and HSV-2 is the varicella-zoster virus (VZV), the herpes virus that causes chickenpox and shingles. VZV is spread via physical contact; once infected, the virus lives dormant in the body forever.
Chickenpox is infectious one to two days before the rash starts and until the blisters have dried and scabbed over.
What Is Valacyclovir?
Valacyclovir is an orally administered medication that is taken as a swallowable tablet.
It is sold under the brand-name form Valtrex, which contains valacyclovir as its active ingredient. Valtrex is generally safe for most people and carries no black box warning.
Valtrex's (valacyclovir) FDA-approved uses in adults 18 and older include the treatment of:
Cold sores
Genital herpes, including treatment and suppression of the virus in people with compromised immune systems and reduction of transmission
Shingles
Valtrex's (valacyclovir) FDA-approved uses in children and adolescents include the treatment of:
Cold sores
Chickenpox, which commonly shows up in children and is caused by the same virus that leads to shingles in adults
There are some off-label uses (non-FDA-approved) for valacyclovir. Some examples may include times when herpes simplex virus causes skin symptoms, such as sores or blistering in various body areas.
As a result, valacyclovir has been used in the treatment of herpetic whitlow (herpes virus that causes blisters on the skin near fingernails) and herpes gladiatorum (a form of herpes most commonly spread via athletic events involving skin-to-skin contact).
How Does Valacyclovir Work?
Valacyclovir is a prodrug of acyclovir. This means that during consumption, your liver slightly alters the chemical structure of valacyclovir after you swallow it to change it into acyclovir.
Acyclovir suppresses viruses by inserting itself into the growing DNA chain of the virus, stopping growth and decreasing the ability of the virus to make more copies of itself.
What Is Acyclovir?
Acyclovir is sold in various dosage forms, including oral tablets and capsules, an oral suspension, creams, ointment, and even an injectable, subcutaneous (under the skin) form.
Like valacyclovir, acyclovir is generally safe for most people and carries no black box warning.
Additionally, branded versions of acyclovir are also on the market. One such example is Zovirax, which is available as an ointment or cream.
In comparison, the branded drug Sitavig is given via buccal tablets, which are taken by placing them between your gums and cheek.
Acyclovir's FDA-approved uses in adults include:
Cold sores
Genital herpes, including treatment and suppression of the virus in people with compromised immune systems and reduction of transmission
Shingles
In comparison, acyclovir's FDA-approved uses in children and adolescents include:
Cold sores that keep coming back in people 12 and older
Chickenpox
Some examples of off-label uses for acyclovir include acute retinal necrosis (a retinal infection caused by a virus from the herpes family), herpes simplex meningitis (meningitis caused by the herpes virus), and viral encephalitis (infection or inflammation of the brain).
How Does Acyclovir Work?
Acyclovir works the same way as valacyclovir once it is converted to the active form of the drug. It inserts itself into the DNA chain of the herpes virus and inhibits further growth.
This stops the ability of the virus to keep producing more copies of itself.
Dosage Comparison
The following will outline standard dosing recommendations for valacyclovir vs. acyclovir concerning age, weight, indication, and mode of administration:
| Valacyclovir: | Acyclovir: |
Brand Name(s): | • Valtrex | • Zovirax, Sitavig |
Generic Product Available: | • Yes | • Yes |
Dosage Form(s) Available: | • Oral tablets | • Oral capsule |
Typical Adult Dosage: | • Tablet use: 500-2000 milligrams (mg) two to three times per day for 5-10 days | • Tablet use: 200-800 mg every 4 hours for 5-14 days |
Typical Pediatric Dosing: | • For oral herpes (ages 12 and older): 2000 mg twice daily | • Less than 100 pounds: weight-based dosing, 20-30 mg per kilogram (kg) two to four times per day for 5-14 days |
How Fast Do They Work?
You can expect acyclovir and valacyclovir to help cold sores within two to three days and genital herpes in around five days. However, blisters and rashes may take up to a couple of weeks to clear completely.
The sooner you can start taking acyclovir or valacyclovir once symptoms show up, the better the medications will work to treat the outbreak.
It’s also essential to take them exactly as prescribed, several times daily. It may help to set a reminder on your phone so as not to miss doses and potentially reduce the effectiveness of the antiviral.
Comparative Efficacy
Acyclovir and valacyclovir are both effective drugs for speeding up the healing of skin blisters and rashes, as well as pain and other symptoms caused by shingles.
While there exist little head-to-head comparisons of these drugs, one study that featured over 1,000 adult participants showed that valacyclovir helped resolve shingles symptoms faster than acyclovir, with valacyclovir resolving symptoms of shingles in 38 days versus acyclovir's 51 days.
Valacyclovir remains in your system longer than acyclovir, so some people can make it more accessible.
Both drugs work very similarly; generally, one is not recommended over the other.
Alternative Treatment Options
In addition to taking prescription medication, there are things you can do at home to help treat cold sores or other blisters caused by a herpes virus infection.
For example, over-the-counter (OTC) cold sore treatment options exist, such as Abreva (docosanol), Orajel (benzocaine), and Herpecin L (dimethicone/meradimate/octinoxate/octisalate/oxybenzone).
These creams or ointments are applied directly to the cold sore to lessen pain or help treat the sore. Applying these at the first sign of a cold sore is best.
You can also place ice on the cold sore or suck on ice chips to help numb the area. Avoiding certain foods such as tomatoes, citrus fruits, and spicy foods may help prevent the burning if these foods touch a cold sore.
Finally, apply petroleum jelly or another hydrating ointment to the sores and surrounding area to prevent dry and cracked skin.
Side Effects & Precautions
The most common side effects of acyclovir and valacyclovir are mild and usually resolve independently.
However, recorded side effects associated with the use of both drugs have been symptoms of nausea, vomiting, headache, and diarrhea.
Precautions
Although rare, serious side effects are possible with valacyclovir and acyclovir, especially in certain circumstances, including the following:
If you have kidney disease, you may need a lower-than-normal dose of acyclovir or valacyclovir to avoid further kidney damage.
Neurological problems such as agitation, confusion, and hallucinations are more likely in older people taking antivirals like acyclovir or valacyclovir.
If you have a weakened immune system, such as in advanced human immunodeficiency virus (HIV), or if you are a transplant recipient, you may be at higher risk of two conditions called hemolytic uremic syndrome (HUS, when kidney function diminishes due to Escherichia coli [E. coli] infection) and thrombotic thrombocytopenic purpura (TTP, a blood clotting disorder that can damage the kidneys).
Potential for Interaction
Valacyclovir and acyclovir don’t have any known significant interactions with other medications.
However, giving your healthcare provider and pharmacist your current medication list is still essential to check for potential issues.
For example, other medications that cause kidney damage may increase the risk of kidney issues from taking valacyclovir or acyclovir.
Summary
Acyclovir and valacyclovir are both effective antiviral medications that can shorten the time until symptoms you’re experiencing from shingles, genital herpes, or cold sores improve.
Valacyclovir may be simpler for you to take due to its more straightforward dosing schedule, and it also resolved shingles symptoms faster than acyclovir in one study.
Remember that both medications will work better if you start taking them at the first sign of symptoms, such as burning, tingling, or itching.
Your healthcare provider will consider your preferences and other factors to determine your best choice.
Frequently Asked Questions
How do I store valacyclovir vs. acyclovir?
Valacyclovir and acyclovir tablets should be stored at room temperature (between 68 and 77 degrees F) in a well-closed container away from excess heat or moisture.
Store liquid forms of the medicines in the fridge (between 36 and 46 degrees F) and throw away any remaining liquid after 28 days.
Keep all acyclovir and valacyclovir out of reach of children.
Is my genital herpes still contagious while taking valacyclovir or acyclovir?
Yes, if you have genital herpes, you are still contagious while taking valacyclovir or acyclovir. Remember, these drugs reduce the risk of virus transmission but do not eliminate the risk.
As a result, you should use protection, including condoms, during sexual intercourse.
Read the original article on Verywell Health.
