Hygroscopicity of Cefazolin Sodium: Application to Evaluate the Crystallinity of Freeze-Dried Products

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Abstract
The hygroscopicity behavior of the pentahydrate, monohydrate, amorphous, and dehydrated forms of solid cefazolin sodium (CEZ) was studied under different relative humidity (RH) conditions. Between 42 and 86% RH, the pentahydrate (α form), the monohydrate, and their dehydrated forms absorbed atmospheric moisture equivalent to their hydrate numbers. The pentahydrate demonstrated a hysteresis effect at 15 and 31% RH. On the other hand, the water content of the amorphous form increased linearly with increases in RH. The noncrystalline state was maintained below 56% RH. For the dehydrated α form there was a distinct birefringence when viewed under polarizing light, the X-ray diffraction pattern was weak and diffuse, and the infrared (IR) spectra were discernibly different from that of the amorphous form. The freeze-dried CEZ showed hygroscopic behavior almost similar to that of the dehydrated α form. Two-component mixtures of various CEZ forms showed a linear relationship between the water content and the mixing ratio when stored at 31, 42, and 56% RH. From the hygroscopicity data, the crystallinity of freeze-dried CEZ could be estimated as the percentage of the dehydrated α form.