Active Ingredients

Valaciclovir – Effect, Application & Risks


Valaciclovir is one of the most commonly used drugs to fight herpes simplex virus infection and shingles . The drug is processed in numerous preparations, represents a prodrug and is considered an antiviral .

What is valacyclovir?

Valaciclovir is a prodrug of aciclovir , which is used to treat herpes infections and shingles. The term prodrug describes substances that – like valaciclovir – do not bring about any immediate effects or successes themselves, but only begin to take effect inside the body. In this way, valaciclovir is converted in the human body to the active ingredient aciclovir, which then kills herpes viruses.

The property as a prodrug gives valaciclovir numerous advantages. For example, a bad taste is avoided, the solubility increased and the bioavailability of the active ingredient increased. In addition, valaciclovir is absorbed more rapidly than similar non-prodrug compounds.

In chemistry, the active ingredient is described by the molecular formula C 13 – H 20 – N 6 – O 4. Valaciclovir thus has a moral mass of 324.34 g/mol.

Pharmacological effect on body & organs

From a pharmacological point of view, valaciclovir is not only an antiviral, but also a prodrug. The active ingredient is rapidly absorbed in the human intestine , so that the bioavailability is significantly improved compared to similar drugs. The literature reports an availability of around 55%, which is more than five times the average value of 10%.

After absorption by the body, valaciclovir is converted to the active form aciclovir. This is done by metabolism ( metabolization ). Aciclovir is closely related to the nucleobase guanine , which is a component of DNA and RNA. This enables the substance to penetrate the metabolism of cells and switch them off. It does this by making it impossible for the virus to spread its DNA.

The special feature of aciclovir is that it only works where it is actually needed. Because the active ingredient only attacks cells that are already infected by the virus.

Due to the mechanism of action, valaciclovir is regarded as a virostatic agent that has antiviral properties against various herpes viruses (including simplex and zoster).

Medicinal Application & Use for Treatment & Prevention

Compared to other antivirals used to combat herpes, the field of application of valaciclovir is very wide. Because the substance is effective against almost all herpes viruses.

The most common types against which valaciclovir is used include cold sores (in the professional world: herpes simplex), shingles and chickenpox (varicella-zoster virus), glandular fever , which is triggered by the Epstein-Barr virus , as well as of the cytomegalovirus . Genital herpes can also be treated with valaciclovir.

The dosage required in each case depends on the respective underlying disease and the individual patient, so that the medical instructions for use must always be observed. However, usually 1000 mg three times a day is adequate for a healthy adult. The appropriate dose for children and adolescents under 12 years of age is lower.

Valaciclovir is most commonly administered in tablet form. These are taken orally by the patient with sufficient water. The best-known preparations containing valaciclovir include Valtrex® in Germany, Austria and Switzerland, as well as Valaciclomed® and Valdacir®, which are only sold in Austria. There are also numerous generics .

Risks & side effects

Undesirable side effects can occur after taking valaciclovir . However, this is not necessarily the case. The most common side effects include headaches , nausea , dizziness and a general feeling of being unwell .

Occasionally, after taking valaciclovir, there may also be problems with the gastrointestinal tract . These are noticeable through abdominal pain , diarrhea , vomiting or slight cramps . A state of confusion or skin reactions such as itching , a rash or redness can also occur. In addition, the occurrence of photosensitivity is possible. Kidney failure or functional disorders of the same occur very rarely .

Valaciclovir should not be taken if hypersensitivity or allergy is known. In addition, attention must be paid to interactions. Valaciclovir is actively secreted in the kidneys via so-called organic anion transporters (OAT), which is why interdependencies with other organic anions such as probenecid are conceivable.

Particular caution is also required in the case of a combination with substances that are toxic to the kidneys. The doctor must always be kept informed about all the preparations taken in order to minimize the risk of interactions.

Lisa Newlon
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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.