Valacyclovir Hydrochloride

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Cat Number

API0232084

CAS Number

124832-27-5

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Product Detail Description Scientific Support Customer Q&A

CAS Number

124832-27-5

EINECS

641-092-8

Storage

Store at room temperature

Synonyms

Valacyclovir HCl; Valaciclovir hydrochloride; 256U87 hydrochloride; BW-256U87; DTXSID2044210; NSC-759101; G447S0T1VC

Molecular Formula

C13H21ClN6O4

Molecular Weight

360.8

Smiles

CC(C)[C@@H](C(=O)OCCOCN1C=NC2=C1N=C(NC2=O)N)N.Cl

Appearance

White to off-white crystalline powder

Melting Point

170-172°C

Boiling Point

588.4°C at 760 mmHg

Relative Density

1.55

General Description

Valacyclovir hydrochloride is the L‑valyl ester prodrug of acyclovir, designed to overcome the poor oral bioavailability of its parent compound. The molecule incorporates a valine moiety that targets intestinal peptide transporters (PEPT1) for active absorption. Once inside the body, the ester linkage is cleaved, releasing acyclovir. This chemical modification results in three‑ to five‑fold greater systemic exposure compared to acyclovir.

Mechanism of Action

Following rapid conversion to acyclovir, the drug is phosphorylated first by viral thymidine kinase (in herpesvirus‑infected cells) and subsequently by host cellular kinases to acyclovir triphosphate. This metabolite competitively inhibits viral DNA polymerase and is incorporated into growing viral DNA strands, causing chain termination. The high specificity for virus‑infected cells explains its selective antiviral activity and low host cell toxicity.

Application

Valacyclovir is indicated for the treatment of herpes zoster (shingles), herpes simplex virus infections (including genital herpes and cold sores), and for suppression of recurrent genital herpes. It is also used for the reduction of cytomegalovirus (CMV) disease following solid organ transplantation. The drug demonstrates efficacy against varicella‑zoster virus, herpes simplex types 1 and 2, and Epstein‑Barr virus, with higher intracellular concentrations achieved than with acyclovir.

The Zoster Eye Disease Study (ZEDS) randomized 527 immunocompetent adults with a history of herpes zoster ophthalmicus to 12 months of suppressive valacyclovir (1000 mg daily) or placebo. The primary endpoint — time to first new or worsening keratitis or iritis within 12 months — was not met (HR 0.77, 95% CI 0.56‑1.05, P=0.09). However, at the secondary 18‑month time point, valacyclovir significantly reduced the occurrence (HR 0.73, P=0.03). Multiple episodes of keratitis or iritis were also fewer at both 12 and 18 months. The authors conclude that one year of suppressive valacyclovir should be considered for this condition.

Fig. 1 Kaplan-Meier Curve of Time to First Occurrence of Confirmed End Point by Treatment Group in Each Strata. (Cohen EJ, et al., 2025)

References

Cohen EJ, et al. Low-Dose Valacyclovir in Herpes Zoster Ophthalmicus: The Zoster Eye Disease Randomized Clinical Trial. JAMA Ophthalmol. 2025;143(4):269-276.

Does Valacyclovir Hydrochloride require protection from moisture during storage?

Yes, it is slightly hygroscopic and can hydrolyze to acyclovir and valine. Store in tightly sealed, moisture-proof containers with desiccant.

What is the recommended storage temperature for Valacyclovir Hydrochloride?

Store at controlled room temperature (15-25°C). Avoid temperatures above 30°C, which accelerate hydrolysis of the valyl ester.

Is Valacyclovir Hydrochloride stable in tablet formulations with common excipients?

Yes, when formulated with moisture-protective packaging (e.g., blisters or HDPE bottles with desiccant).

How is the impurity acyclovir (the active moiety) monitored during stability?

This primary hydrolysis product is specifically quantified using a stability-indicating HPLC method, ensuring it remains well below ICH limits.