Acyclovir vs. Valacyclovir

Acyclovir vs. Valacyclovir
Published : Feb 04, 2024
Last Updated : Feb 06, 2024

There are several antiviral medicines that treat herpes and cold sores. However the most effective, popular, and widely prescribed medicines by doctors are Acyclovir and Valacyclovir.

It is important to know that herpes is extremely infectious and spreads through close contact like sexual activity.

Cold sores are small painful blisters that appear on your lips or around the mouth.

People suffer from cold sores due to type one herpes simplex virus (HSV-1). Cold sores are often spread by sharing the towels, utensils, or razors of an infected person.

You need to understand that cold sores can’t be cured but can manage outbreaks via herpes medicines such as Acyclovir and Valacyclovir.

Acyclovir and Valacyclovir are prescription medicines helpful in treating herpes infections like cold sores and genital herpes. Both medicines work in the same way.

They help in stopping the herpes virus from spreading & multiplying but there are some differences between both medicines.

What is Acyclovir?

Acyclovir is an antiviral medicine that treats herpes infections. It works in your body by preventing the virus from multiplying.

When you are infected for the first time or the herpes virus reactivates itself, it starts to spread through your skin cells.

The virus makes use of the cell’s natural DNA copying procedure to make copies of itself so that it can attack and infect other cells. 

However, Acyclovir stops this work. It helps in blocking an enzyme known as DNA polymerase from working. This is the enzyme that is required to copy the virus’s DNA.

It mimics this enzyme taking its place but then starts working differently. This further slows how quickly the virus spreads and gives your immune system a better chance to clear it from the skin cells.

Acyclovir comes in pill form and is swallowed with a glass of plain water. To apply directly to your infected skin, you can also purchase creams that contain acyclovir.

What is Valacyclovir?

Valacyclovir is the same antiviral medicine as acyclovir. You can take it to manage the infection of herpes, decrease the seriousness of outbreaks, and avoid outbreaks from happening.

It is necessary to know that valacyclovir is the generic name for the medicine and you can also purchase a branded version known as Valtrex. Valacyclovir works in the same way as acyclovir.

It obstructs the enzyme DNA polymerase from working and prevents the virus from imitating itself. It works in the same way as you use valacyclovir i.e., your body converts it into acyclovir.        

Acyclovir vs. valacyclovir: What are the differences?

Acyclovir is prescribed by the doctor for the treatment of herpes simplex virus and varicella-zoster virus. It belongs to the class of antiviral medicines called synthetic purine deoxynucleoside analogs.

Acyclovir fights against viral infections by including itself in the viral DNA and then keeping out viral DNA synthesis.

You need to know that acyclovir is available in different forms like topical cream, ointment, solution for injection, ophthalmic ointment, oral tablets, oral capsules, oral suspension, and oral dissolving tablets.    

The oral acyclovir formulation comes with weak bioavailability as it is changed in first-pass metabolism. As a result, there is poor absorption from your gastrointestinal tract.  

Valacyclovir (Valtrex) is also a prescription antiviral medicine. Valacyclovir is considered the L-valyl ester of acyclovir. Also, it is considered as the prodrug of acyclovir.

First-pass metabolism eliminates most of the acyclovir from circulation and this is the reason why the oral bioavailability is low for acyclovir. You need to know that first-pass metabolism converts valacyclovir to available acyclovir then to the body.

When taking acyclovir, the oral bioavailability is only 10-20% and the oral bioavailability of valacyclovir is high as 54%. The procedure of first-pass metabolism also produces differences in how often the dosage of these medicines must be taken.   

Acyclovir must be dosed almost three to five times regularly as per the indication of the doctor.

However, valacyclovir is taken once or twice regularly according to the prescription. You can find Valacyclovir in oral tablets and in two different strengths i.e., 500mg and 1000mg.


Can acyclovir and valacyclovir treat all types of herpes?

It is vital to know that both acyclovir and valacyclovir are effective against all types of herpes virus, with different doses that treat outbreaks of shingles, genital herpes, and oral herpes. 

Although, most doctors recommend acyclovir and valacyclovir for treating herpes condition because of their easier doing.

Is valacyclovir stronger than acyclovir?

Though valacyclovir is not stronger than acyclovir it is absorbed by your body more efficiently when compared to acyclovir. This further means that valacyclovir makes it into your system in a more effective way.  

Is it safe to take acyclovir and valacyclovir together?

No, it is not recommended to take acyclovir and valacyclovir at the same time. Valacyclovir is converted inside the body into acyclovir. So, taking both medicines can cause serious risks. It will increase the risk of side effects and even damage your kidneys.

Make sure you take these medicines exactly in the same way as directed by the doctor.

What are the warning signs of acyclovir and valacyclovir?

Both acyclovir and valacyclovir are contraindicated in patients who have a history of allergic reactions to any of these medicines. If a patient suffers from any kind of prior reaction to famciclovir, penciclovir, ganciclovir or valganciclovir cautions need to be taken because there is a chance of cross-sensitivity between both medicines.    

In patients suffering from renal dysfunction, both Acyclovir and Valacyclovir Tablets must be taken carefully. Dose adjustments might be important in order to avoid the problem of central nervous system toxicity. 

Thus, if you suffer from herpes or cold sores, the best way is to speak to the doctor to know about the treatment options. Depending upon your symptoms, overall health, immune system, and lifestyle, the doctor will give you advice about the medicine.