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Valacyclovir vs Acyclovir

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Valacyclovir Information

Acyclovir Information

Comparative Analysis

Valacyclovir Prescription Information

Acyclovir Prescription Information

Valacyclovir Side Effects

Acyclovir Side Effects

Safety Information

Cost Information

Market Information



For patients with viral infections such as herpes simplex and varicella-zoster, certain antiviral drugs that inhibit the replication of virus particles within host cells can help in managing symptoms and reducing the duration of outbreaks. Valacyclovir and Acyclovir are two such drugs that are prescribed for these conditions. They each impact different stages of the viral life cycle but both have been proven effective in treating herpes-related infections. Valacyclovir is a prodrug, meaning it converts into acyclovir once ingested to block DNA synthesis, thereby inhibiting viral replication. Acyclovir, on the other hand, primarily works by directly penetrating infected cells to interrupt the chain reaction mechanism during DNA duplication - thus preventing further spread of infection.

Valacyclovir vs Acyclovir Side By Side

Brand NameValtrexZovirax
ContraindicationsAllergic reaction to valacyclovir, kidney disease, weakened immune systemsAllergic reaction to acyclovir, kidney disease, weakened immune systems
CostAverages at about $1-$3/day for genericAverages from about $0.20-$0.80/day for generic
Generic NameValacyclovirAcyclovir
Most Serious Side EffectSigns of an allergic reaction, unusual changes in the amount or color of your urine, difficulty speaking or swallowing, severe stomach/abdominal pain, yellowing eyes/skin (jaundice), easy bruising/bleedingSigns of a severe allergic reaction, unusual changes in mood or behavior, kidney problems, easy bruising or bleeding, severe stomach/abdominal pain, persistent nausea/vomiting, yellowing eyes/skin, dark urine
Severe Drug InteractionsNot specified in the articleNot specified in the article
Typical Dose500–1000 mg twice daily200 mg five times daily

What is Valacyclovir?

Valacyclovir (also known as Valtrex) and Acyclovir (Zovirax), both are antiviral medications used to treat infections caused by certain types of viruses. Valacyclovir, a prodrug of acyclovir, is more easily absorbed by the body and can be taken fewer times during the day compared to acyclovir. It was approved by FDA in 1995. Once inside the body, it gets converted into acyclovir, blocking the action of viral DNA polymerase – an enzyme essential for the virus to multiply – thus preventing its spread within your body. Both medications are prescribed for treating conditions such as herpes zoster (shingles), cold sores around mouth and outbreaks of genital herpes. However, valacyclovir has a higher bioavailability than acyclovir which makes it more effective with less frequent dosages but might also lead to slightly stronger side effects.

What conditions is Valacyclovir approved to treat?

Valacyclovir is approved for the management of several types of viral infections:

  • Herpes simplex, including initial and recurrent genital herpes
  • Reduction of transmission of genital herpes in patients with a history of 9 or fewer recurrences per year
  • Herpes zoster (shingles) in immunocompetent adults
  • Chickenpox in immunocompetent pediatric patients aged 2 to less than 18 years

How does Valacyclovir help with these illnesses?

Valacyclovir helps to manage viral infections such as herpes simplex and varicella-zoster by blocking the replication of the virus's DNA. It does this by becoming incorporated into new viral DNA chains, preventing them from lengthening any further. This stops the production of new viruses within infected cells. Valacyclovir is actually a prodrug of acyclovir, which means it is converted into acyclovir in the body. The advantage of valacyclovir over acyclovir is its better absorption rate, meaning that lower doses can be used to achieve effective concentrations in the blood stream. Both drugs are antiviral agents that play an important role in managing symptoms and reducing outbreaks for those infected with these types of viruses.

What is Acyclovir?

Acyclovir, available under the brand name Zovirax among others, is an antiviral medication primarily used for the treatment of herpes simplex virus infections, chickenpox, and shingles. It was first approved by the FDA in 1981. Acyclovir works by inhibiting DNA synthesis in viruses more than human cells due to its greater affinity to viral thymidine kinase enzyme. This means that it stops the spread of infection within your body without causing significant harm to your own cells.

It's worth noting that while acyclovir doesn't cure these viral diseases, it can reduce symptoms and speed up recovery. As with other antiviral medications, side effects vary but common ones include nausea and diarrhea. While generally well-tolerated in most people compared to many other drugs intended for similar purposes (like Valacyclovir), those with kidney conditions may need dosage adjustments.

What conditions is Acyclovir approved to treat?

Acyclovir is an antiviral medication that has been approved for the treatment of several herpes-related conditions, including:

  • Genital Herpes: Acyclovir can reduce the frequency and severity of outbreaks.
  • Oral Herpes (also known as Cold Sores or Fever Blisters): The medication can be used to treat active outbreaks or prevent future ones.
  • Shingles: Acyclovir may be prescribed to help manage this painful condition caused by the same virus as chickenpox.
  • Chickenpox: While less common today due to vaccination, acyclovir may still be used in certain cases for children who develop severe symptoms.

How does Acyclovir help with these illnesses?

Acyclovir is an antiviral medication that works by slowing the growth and spread of the herpes virus in the body. This allows the immune system to effectively combat viral infection, reducing symptoms such as burning, itching, and sores associated with herpes outbreaks. It's important to note that Acyclovir does not cure herpes or prevent transmission; it simply assists in managing symptoms. Its action on DNA polymerase enzyme may play a critical role in its effectiveness against viruses. In comparison to Valacyclovir, which is essentially a prodrug converted into Acyclovir in the body after ingestion, Acyclovir requires more frequent dosing due to its shorter half-life but can be equally effective when taken appropriately. Therefore, while Valacyclovir might provide convenience with less frequent dosing schedules, Acyclovir remains a robust choice for patients who require flexibility or have specific needs regarding their antiviral treatment.

How effective are both Valacyclovir and Acyclovir?

Both valacyclovir and acyclovir have proven track records in treating viral infections like herpes simplex, and they were both approved by the FDA within a decade of each other. Since these drugs act on the same virus but are metabolized differently, they may be prescribed under different circumstances. The effectiveness of valacyclovir and acyclovir in managing herpes was directly studied in numerous clinical trials; these two drugs exhibited similar efficacy in managing symptoms as well as comparable safety profiles.

A 2002 review demonstrated that valacyclovir is effective at suppressing genital herpes outbreaks starting from the first week of treatment, thanks to its favorable pharmacokinetic profile which allows for less frequent dosing compared to acyclovir (usually three times daily versus five times daily). This makes it preferred by some patients due to increased convenience. Additionally, it has been reported that valacyclovir effectively diminishes transmission rates among discordant couples where one partner is diagnosed with genital herpes.

A comprehensive analysis published in 2016 indicated that while both antiviral medications are more effective than placebo treatments for various types of viral conditions including shingles and cold sores, there doesn't seem to be much difference between them when considering their overall effectiveness for most patients. However, because acyclovir requires more frequent administration throughout the day compared to valacyclovir's simpler regimen, this might sway preference toward using valacyclovir simply due to ease-of-use considerations.

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At what dose is Valacyclovir typically prescribed?

Oral dosages of Valacyclovir for treating herpes outbreak range from 500–1000 mg twice daily, but studies have indicated that 500 mg twice daily is sufficient for most people. Children aged 12 years and older may be started on 500 mg twice daily. In either population, dosage can be increased after a few days if there is no response. The maximum dosage that should not be exceeded in any case is 2000 mg per day. Acyclovir dosing varies based on the condition being treated, with typical doses ranging from 200–800mg taken two to five times per day depending on individual health needs and medical advice.

At what dose is Acyclovir typically prescribed?

Acyclovir treatment typically begins at a dosage of 200 mg five times daily, with doses spaced approximately every four hours, omitting the night-time dose. For severe initial clinical episodes of herpes simplex infections, this can be increased up to 400 mg. The maximum daily dose is 2000 mg divided into five doses and if there's no response to this treatment after a few weeks, your doctor may need to reassess your condition and consider alternative options. Always remember that the dosing regimen must be adjusted depending on renal function status.

What are the most common side effects for Valacyclovir?

Common side effects of valacyclovir include:

  • Nausea
  • Stomach pain
  • Dizziness
  • Headache
  • Feeling very tired

While acyclovir shares some similar side effects, such as nausea and headaches, it also has some unique ones:

  • Diarrhea
  • General body discomfort (malaise)
  • Increased heart rate
  • Joint or muscle pain
  • Skin rash

These lists are not exhaustive and other symptoms may occur. If you experience any unusual or severe symptoms while taking either medication, seek immediate medical attention.

abstract image of a patient experiencing side effect

Are there any potential serious side effects for Valacyclovir?

While both Valacyclovir and Acyclovir are antiviral medications used to treat infections caused by certain viruses, they may sometimes cause side effects. Here are some potential serious side effects that you should be aware of when taking either of these drugs:

  • Signs of an allergic reaction, such as hives; difficulty breathing; swelling in your face, throat, or tongue
  • Unusual changes in the amount or color of your urine
  • Unexpected weight gain or loss
  • Difficulty speaking or swallowing
  • Severe stomach/abdominal pain
  • Yellowing eyes/skin (jaundice)
  • Easy bruising/bleeding

Also note symptoms related to mental/mood changes like agitation and hallucinations. If you notice any severe dizziness, fainting spells, unusually slow or rapid heartbeat, seizures or unusual tiredness immediately seek medical attention.

Remember this isn't a complete list; both Valacyclovir and Acyclovir can have other rare but potentially harmful side effects.

What are the most common side effects for Acyclovir?

Acyclovir, another commonly used antiviral drug, can also cause certain side effects. These may include:

  • Nausea or vomiting

  • Diarrhea

  • General ill feeling

  • Headache or light-headedness

  • Skin rashes

  • Tiredness and sleep problems (insomnia) Moreover, Acyclovir may occasionally lead to more severe side effects such as:

    • Kidney problems (little or no urination, painful or difficult urination)
    • Easy bruising or bleeding
    • Unusual weakness Always consult with a healthcare professional when choosing between Valacyclovir and Acyclovir for the treatment of viral infections.

Are there any potential serious side effects for Acyclovir?

While Acyclovir is generally well-tolerated, in some rare cases it can lead to serious side effects. These may include:

  • Signs of a severe allergic reaction such as hives; difficulty breathing; swelling of your face, lips, tongue or throat.
  • Unusual changes in mood or behavior including agitation, confusion and hallucinations.
  • Symptoms that could indicate kidney problems such as pain in the lower back, difficult or painful urination and changes in the amount of urine.
  • Easy bruising or bleeding
  • Severe stomach/abdominal pain
  • Persistent nausea/vomiting
  • Yellowing eyes/skin
  • Dark urine

These are not all the possible side effects. If you experience any other symptoms which you think may be due to this medicine, speak with your doctor immediately for medical advice.

Contraindications for Valacyclovir and Acyclovir?

Both Valacyclovir and Acyclovir, as with most other antiviral medications, may cause side effects in some people. If you notice symptoms such as unusual changes in mood or behavior, confusion, hallucinations, agitation or seizures after taking either medication, please seek immediate medical attention.

Neither Valacyclovir nor Acyclovir should be taken if you have had an allergic reaction to them in the past. Always inform your physician about all the medications you are currently taking; this includes prescription drugs, over-the-counter medicine and any supplements that could potentially interact with these antiviral drugs.

In particular caution is required for those suffering from kidney disease or weakened immune systems - both common conditions among older adults - due to potential adverse reactions with these medicines. Hydration status also plays a key role when using these drugs; insufficient water intake can lead to kidney problems while on therapy. Hence it's crucial not only to communicate all your health details but also maintain adequate hydration when under treatment involving Valacyclovir or Acyclovir.

How much do Valacyclovir and Acyclovir cost?

For the brand name versions of these drugs:

  • The price of 30 tablets of Valtrex (valacyclovir, 500 mg) averages around $200, which works out to approximately $6.67 per day.
  • The price for a similar amount of Zovirax (acyclovir, 400 mg) is about $225, equating to roughly $7.50 per day.

Thus, if you are on higher dosages for acyclovir or valacyclovir (i.e., above the standard dose), then Valtrex may be less expensive on a per-day treatment basis than Zovirax. However, cost should not be your primary consideration when deciding between these two antiviral medications.

The generic versions of both drugs significantly reduce costs:

  • Valacyclovir can typically be found in packs ranging from 10 to 90 tablets with prices varying widely across retailers but averaging at about $1-$3/day.
  • Acyclovir's cost varies as well depending on the retailer and quantity purchased but its average daily cost ranges from about $0.20-$0.80/day.

These drugs have different efficacy profiles and side effects that need consideration beyond just their pricing differences.

Popularity of Valacyclovir and Acyclovir

Valacyclovir and Acyclovir are two effective antiviral medications, primarily used to treat herpes simplex virus (HSV) type 1 and 2, as well as varicella-zoster virus (VZV), the cause of chickenpox and shingles.

In its generic form, Valacyclovir was prescribed approximately 3.7 million times in the USA in 2020. This represented around a third of all prescriptions for antiviral medications intended to treat HSV and VZV. Its use has been moderately increasing since it first came onto the market.

On the other hand, Acyclovir saw about 8 million prescriptions filled in that same year. It accounts for just under half of all HSV/VZV targeted antiviral prescriptions in the US due to its longer history on the market compared to valacyclovir. The prevalence of acyclovir usage has remained steady over recent years.


Both valacyclovir and acyclovir are antiviral medications commonly prescribed for the treatment of herpes simplex virus infections, including cold sores and genital herpes. They have a strong track record of effectiveness supported by numerous clinical studies and meta-analyses showing they are more effective than placebo treatments. These drugs aren't typically combined due to their similar mechanisms of action - both work by inhibiting viral DNA replication.

Valacyclovir is often considered the first-line treatment option because it provides a higher bioavailability compared to acyclovir, which means that it's better absorbed into the bloodstream. This allows for less frequent dosing with valacyclovir, making it a more convenient choice for many patients.

Both medications are available in generic form providing significant cost savings especially for out-of-pocket payers. Like most drugs, there may be an adjustment period where effects might not be immediately noticeable as your body adapts to them.

The side effect profile between these two antiviral agents is fairly comparable; common side effects include nausea, headache and abdominal pain. Both medications are generally well-tolerated but can cause kidney complications in rare cases - hence why hydration is important during treatment. As with any medication regime, patients should closely monitor their symptoms when starting therapy and seek medical attention promptly if they notice worsening or unexpected side effects.