chemistry

Valaciclovir

Valaciclovir is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Valaciclovir rather than just read about it. In short: Valaciclovir, also spelled valacyclovir, is an antiviral medication used to treat outbreaks of herpes simplex or herpes zoster (shingles). It is also used to prevent cytomegalovirus following a kidney transplant in high risk cases.

Key takeaways

Valaciclovir belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Valaciclovir to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Valaciclovir from memory before moving on to harder problems.

Reference excerpt

Valaciclovir, also spelled valacyclovir, is an antiviral medication used to treat outbreaks of herpes simplex or herpes zoster (shingles). It is also used to prevent cytomegalovirus following a kidney transplant in high risk cases. It is taken by mouth. Common side effects include headache and vomiting. Severe side effects may include kidney problems. Use in pregnancy appears to be safe. It is a prodrug, which works after being converted to aciclovir in a person's body. Valaciclovir was patented in 1987 and came into medical use in 1995. Valaciclovir is a therapeutic alternative on the World Health Organization's List of Essential Medicines. It is available as a generic medication. In 2023, it was the 98th most commonly prescribed medication in the United States, with more than 7 million prescriptions.

Medical uses

Valaciclovir is used for the treatment of HSV and VZV infections, including:

Oral and genital herpes simplex (treatment and prevention) Reduction of HSV transmission from people with recurrent infection to uninfected individuals Herpes zoster (shingles): the typical dosage for treatment of herpes is 1,000 mg orally three times a day for seven consecutive days. Prevention of cytomegalovirus following organ transplantation Prevention of herpesviruses in immunocompromised people (such as those undergoing cancer chemotherapy) Chickenpox in children (ages 2–18) It has shown promise as a treatment for infectious mononucleosis and is preventively administered in suspected cases of herpes B virus exposure. Bell's palsy does not seem to benefit from using valaciclovir as its only treatment.

Adverse effects Common adverse drug reactions (≥1% of people) associated with valaciclovir are the same as for aciclovir, its active metabolite. They include: nausea, vomiting, diarrhea and headache. Infrequent adverse effects (0.1–1% of patients) include: agitation, vertigo, confusion, dizziness, edema, arthralgia, sore throat, constipation, abdominal pain, rash, weakness and/or renal impairment. Rare adverse effects (<0.1% of patients) include: coma, seizures, neutropenia, leukopenia, tremor, ataxia, encephalopathy, psychotic symptoms, crystalluria, anorexia, fatigue, hepatitis, Stevens–Johnson syndrome, toxic epidermal necrolysis and/or anaphylaxis.

Pharmacology Valaciclovir is a prodrug, an esterified version of aciclovir that has greater oral bioavailability (about 55%) than aciclovir. It is converted by esterases to the active drug, aciclovir, and the amino acid valine via hepatic first-pass metabolism. Aciclovir is selectively converted into a monophosphate form by viral thymidine kinase, which is more effective (3000 times) in phosphorylation of aciclovir than cellular thymidine kinase. Subsequently, the monophosphate form is further phosphorylated into a disphosphate by cellular guanylate kinase and then into the active triphosphate form, aciclo-GTP, by cellular kinases.

Mechanism of action Aciclo-GTP, the active triphosphate metabolite of aciclovir, is a very potent inhibitor of viral DNA replication. Aciclo-GTP competitively inhibits and inactivates the viral DNA polymerase. Its monophosphate form also incorporates into the viral DNA, resulting in chain termination. It has also been shown that the viral enzymes cannot remove aciclo-GMP from the chain, which results in inhibition of further activity of DNA polymerase. Aciclo-GTP is fairly rapidly metabolized within the cell, possibly by cellular phosphatases. Aciclovir is active against most species in the herpesvirus family. In descending order of activity:

Herpes simplex virus type I (HSV-1) Herpes simplex virus type II (HSV-2) Varicella zoster virus (VZV) Epstein–Barr virus (EBV) Cytomegalovirus (CMV) The drug is predominantly active against HSV and, to a lesser extent, VZV. It is only of limited efficacy against EBV and CMV. However, valaciclovir has been shown to lower or eliminate the presence of the Epstein–Barr virus in subjects afflicted with acute mononucleosis, leading to a significant decrease in the severity of symptoms. Valaciclovir and acyclovir act by inhibiting viral DNA replication, but as of 2016 there was little evidence that they are effective against Epstein–Barr virus. Acyclovir therapy does prevent viral latency, but has not proven effective at eradicating latent viruses in nerve ganglia. As of 2005, resistance to valaciclovir has not been significant. Mechanisms of resistance in HSV include deficient viral thymidine kinase and mutations to viral thymidine kinase and/or DNA polymerase that alter substrate sensitivity. It also is used for herpes B virus postexposure prophylaxis.

Chemistry Details of the synthesis of valaciclovir were first published by scientists from the Wellcome Foundation.

Aciclovir was esterified with a carboxybenzyl protected valine, using dicyclohexylcarbodiimide as the dehydrating agent. In the final step, the protecting group was removed by hydrogenation using a palladium on alumina catalyst.

History Valaciclovir was patented in 1987 and came into medical use in 1995. It is available as a generic medication. In 2022, it was the 113th most commonly prescribed medication in the United States, with more than 5 million prescriptions.

Society and culture

Brand names It is marketed by GlaxoSmithKline under the brand names Valtrex and Zelitrex. Valaciclovir has been available as a generic drug in the US since November 2009.

References

Illustrations

Valtrex brand valaciclovir 500mg tablets

Worked examples

Example 1 — a first encounter with Valaciclovir

Start with the simplest possible case. Write down what Valaciclovir claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Valaciclovir before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Valaciclovir ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Valaciclovir

In research: Valaciclovir appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Valaciclovir in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Valaciclovir is common in secondary-school and first-year university syllabi. It links to neighbouring topics Amino acid derivatives, Anti-herpes virus drugs, Carboxylate esters, so understanding it makes those chapters shorter.
In everyday life: Look for Valaciclovir outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Valaciclovir in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Valaciclovir means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Valaciclovir out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Valaciclovir in simple terms?

Why does Valaciclovir matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Valaciclovir?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Valaciclovir.