Valtrex Drug Description

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Valtrex - Drug Description [Valacyclovir]

DESCRIPTION

VALTREX Caplets (valacyclovir hydrochloride) is the hydrochloride salt of L-valyl ester of the antiviral drug acyclovir (ZOVIRAX Brand, GlaxoSmithKline).
VALTREX Caplets are for oral administration. Each caplet contains valacyclovir hydrochloride equivalent to 500 mg or 1 gram valacyclovir and the inactive ingredients carnauba wax, colloidal silicon dioxide, crospovidone, FD&C Blue No. 2 Lake, hypromellose, magnesium stearate, microcrystalline cellulose, polyethylene glycol, polysorbate 80, povidone, and titanium dioxide. The blue, film-coated caplets are printed with edible white ink. The chemical name of valacyclovir hydrochloride is L-valine, 2-[(2-amino-1,6-dihydro-6-oxo-9H-purin-9-yl)methoxy]ethyl ester, monohydrochloride.

Valacyclovir hydrochloride is a white to off-white powder with the molecular formula C13H20N6O4?HCl and a molecular weight of 360.80. The maximum solubility in water at 25C is 174 mg/mL. The pka?s for valacyclovir hydrochloride are 1.90, 7.47, and 9.43.

MICROBIOLOGY

Mechanism of Antiviral Action

Valacyclovir hydrochloride is rapidly converted to acyclovir which has demonstrated antiviral activity against herpes simplex virus types 1 (HSV-1) and 2 (HSV-2) and varicella-zoster virus (VZV) both in vitro and in vivo. The inhibitory activity of acyclovir is highly selective due to its affinity for the enzyme thymidine kinase (TK) encoded by HSV and VZV. This viral enzyme converts acyclovir into acyclovir monophosphate, a nucleotide analogue.

The monophosphate is further converted into diphosphate by cellular guanylate kinase and into triphosphate by a number of cellular enzymes. In vitro, acyclovir triphosphate stops replication of herpes viral DNA. This is accomplished in 3 ways: