Abstract
LVSEM permits the examination of materials with reduced radiation damage and high contrast, factors which are critical to the successful examination of organic crystals. In this study, LVSEM was applied to characterize the structure of a beam sensitive anhydrous crystal form and its subsequent conversion to the hemihydrate form in an aqueous suspension.Nevirapine, a dipyridodiazepenone compound, is a reverse transcriptase inhibitor currently being developed for the treatment of AIDS. Nevirapine exists as the hemihydrate stable form and as the anhydrous metastable form. The hemihydrate crystals are multifaceted blades (Fig. 1) whereas the anhydrous form exists predominately as large agglomerates of porous “coral like” crystals with high surface area (Fig. 2). When formulated in aqueous suspensions, anhydrous Nevirapine converted into the hemihydrate form, with eventual growth of the hemihydrate crystals. The extent of conversion and rate of growth have been determined to be a function of temperature and time. LVSEM was used to study the anhydrous-to-hemihydrate conversion as the two forms could easily be identified by their characteristic morphology.
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