Mahmoud Mirmehrabi et. al.
Crystal Growth and Design (American Chemical Society), 6(1), 141-149
Different characterization methods (optical microscopy, Karl Ficher titration (KF), XRPD, and solid-state FTIR) were used to identify the two polymorphs and one hydrate of stavudine. The two forms are monotropically related, and form 1 is the stable polymorph. The effects of solvent, impurities, supersaturation, and mixing on the polymorphic occurrence of stavudine are investigated in detail. Hydrogen bonding analysis is employed to qualitatively predict the role of the solvent and structurally related impurities (thymine and thymidine) on polymorphism and crystal habit of stavudine crystals. The impurities showed significant changes in the crystal habit and crystal bulk density of stavudine but had no influence on the polymorphic structure. Depending on the degree of supersaturation at T = 25 °C, a specific polymorph or a mixture of forms 1 and 2 was obtained concomitantly.