A Study on the Crystal Transformation Relationships of Valacyclovir Hydrochloride Polymorphs: Sesquihydrate, Form I, and Form II

Abstract

Valacyclovir hydrochloride is a kind of antiviral drug and has several crystal forms including sesquihydrate (SH), anhydrous Form I, and Form II. Here, the dehydration process of SH by heat drying is investigated by powder X‐ray diffraction, differential scanning calorimetry, thermogravimetry analysis, vapor sorption analysis, and ReactRaman spectroscopy, and the dehydration and absorption of crystal water are revealed. The transformations of SH to Form I, Form II to Form I, and SH to Form II in aqueous ethanol suspension are monitored by ReactRaman spectroscopy, and the mechanisms of two different transition processes are defined through the analysis of ReactRaman spectra. The crystal transformation relationship of the mentioned forms is established.