Acyclovir fights viral infections by incorporating itself into the viral DNA and then prohibiting viral DNA synthesis. Acyclovir is available in a variety of forms including topical cream and ointment, ophthalmic ointment, solution for injection, oral capsules, oral tablets, oral dissolving tablets, and oral suspension. The oral acyclovir formulation has poor bioavailability because it is altered in first-pass metabolism, resulting in poor absorption from the gastrointestinal tract.
Valacyclovir is the L-valyl ester of acyclovir. More simply put, it is considered the prodrug of acyclovir. First-pass metabolism removes most of the acyclovir from circulation, and this is why the oral bioavailability is so low for acyclovir. In contrast, first-pass metabolism converts valacyclovir to acyclovir which is then available to the body.
The process of first-pass metabolism also creates differences in how often these drugs must be dosed. Acyclovir must be dosed three to five times daily depending on the indication, and valacyclovir is typically once or twice daily depending on the indication.
Valacyclovir is only available in oral tablets in mg and 1, mg strengths. Acyclovir and valacyclovir are indicated in the treatment of herpes simplex virus type 1 and type 2, as well as varicella-zoster virus.
The most common of these types of viruses are cold sores, genital herpes, chickenpox, and shingles. These drugs also play an important role in the prophylaxis of these types of infections, such as recurrent genital herpes. Acyclovir and valacyclovir are used off-label for the prevention of cytomegalovirus and treatment of ocular infections related to shingles. Acyclovir and valacyclovir were compared in the treatment of first episodes of genital herpes infections in an international double-blind, randomized trial.
Acyclovir was dosed five times daily, and valacyclovir was dosed only twice daily. It found no clinically significant difference in the lesion healing time, duration of pain, or time to loss of all symptoms. Given that, valacyclovir offers the advantage of twice-daily dosing. This decreases pill burden and increases the likelihood that patients will take the regimen as prescribed until completion.
Your doctor will determine what is best to treat a genital herpes infection, but twice-daily dosing may offer an advantage for valacyclovir. In another randomized, double-blind clinical trial , acyclovir and valacyclovir oral tablet doses were compared for a herpes zoster infection, otherwise known as shingles. The results of this study showed valacyclovir significantly accelerated the resolution of pain associated with a shingles rash.
While the rash itself resolved in similar times with either treatment regimen, there were fewer ocular complications in those treated with valacyclovir. Another significant advantage for valacyclovir in this study is that it only needed to be dosed three times per day as compared to five times per day for acyclovir. Ultimately, only your prescriber can determine which treatment option is best for you with an active herpes zoster infection.
Acyclovir is a prescription medication that is covered by both commercial and Medicare prescription insurance plans. Valacyclovir is a prescription medication that is covered by both commercial and Medicare drug insurance plans.
The manufacturer literature lists side effects for acyclovir and valacyclovir by indication and dosing. Dosing is dependent upon the type of viral infection being treated.
Overall post-marketing data is not provided by specific indication and does not give incidence rates. Given the chemical relationship and similarities of the drugs, the side effects are similar as might be expected.
Gastrointestinal effects such as abdominal pain, nausea, vomiting, and diarrhea can occur with either drug. Some of the more serious concerns are the fact that both drugs have been linked to renal failure and an increase in liver hepatic enzymes.
The following list is not intended to be a comprehensive list of side effects. Please consult your pharmacist or other healthcare professional for a more comprehensive list of adverse events.
Acyclovir and valacyclovir are known to have negative effects on both the kidneys and the liver. Valacyclovir works through a complex chemical process that interferes with the mechanism the herpes virus uses to reproduce, preventing it from multiplying and reducing the rate at which the infection spreads. In short, valacyclovir stops the herpes virus from spreading to healthy cells, reducing the effects of the virus. However, it does make the effects of herpes less severe, meaning the sores developed from the virus heal faster and the aches, cold symptoms and other signs of herpes can become less severe.
If you have herpes, valacyclovir reduces the risk of you transmitting the virus to other people. The amount of time required for valacyclovir to control a herpes or chickenpox outbreak varies based on the severity of the outbreak and how soon you take valacyclovir after noticing herpes symptoms. For most initial herpes outbreaks and cases of recurring herpes, valacyclovir takes effect very quickly and provides some level of relief in as little as two to three days.
Generally, the sooner you take valacyclovir after noticing symptoms, the faster it will be to provide relief. Valacyclovir is available as a generic medication or under several brand names. In the United States, valacyclovir is most commonly sold as Valtrex, which is the original trade name for the drug marketed by GlaxoSmithKline.
Today, valacyclovir is available as a generic medication, meaning there are numerous different trade names in use. Most of the companies manufacturing valacyclovir offer it in several doses, including mg and 1,mg tablets. Generally, the most common dosages are as follows:. For adults with shingles, 1,mg of valacyclovir three times daily, for a total of seven days. For adults with cold sores, a dose of 2,mg of valacyclovir is typically used, with a secondary dose of 2,mg within 12 hours.
For adults treating a first outbreak of genital herpes, 1,mg of valacyclovir two times daily for a total of 10 days. Doctors prescribe valacyclovir to treat infections caused by the herpes virus, including genital herpes. Below, we take a closer look at this drug and outline how it differs from acyclovir.
A person can contract an HSV-1 infection through oral-to-oral contact such as kissing. It is also possible to pass on the HSV-1 virus through oral-to-genital contact, which results in genital herpes. People are more contagious when they have a flare-up of the virus and have active sores.
People usually get the HSV-2 virus through sexual contact and can pass on an HSV-2 infection even if they do not have obvious symptoms. Condoms can reduce the risk of passing on genital herpes, but this is not guaranteed. Another form of herpes virus is called the herpes zoster virus, which is more commonly known as shingles.
The varicella-zoster virus VZV , which is also known as chickenpox , lays dormant in the body after the initial infection. In some people, the virus may reactivate as shingles. A person can only become infected with shingles if they have previously had chickenpox. However, someone who has never had chickenpox can become infected with the virus through someone with shingles if they have direct contact with open sores.
Learn more about shingles and how it is spread here. This antiviral drug can also help reduce the risk of transmitting genital herpes to another person. In some cases, individuals may experience severe side effects such as kidney failure and nervous system problems. There are some warnings that come with valacyclovir. Both valacyclovir and acyclovir treat viral herpes infections and both are equally effective.
The table below shows some key differences. Both of these generic medications are covered by most medical insurance plans. However, a person should check with their plan provider to confirm coverage.
A person can only purchase valacyclovir with a prescription from a doctor, but there are many online pharmacies that offer fast and efficient ways to receive medications. When ordering online, websites such as Roman require that a person do one of the following:. Some companies may have other rules that individuals must follow to receive their prescribed medication.
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