Influence of crystal shape on the tableting performance of L-lysine monohydrochloride dihydrate

The purpose of this study is to understand the influence of crystal shape o n the tableting performance of L-lysine monohydrochloride (LMH) dihydrate, using the method of data analysis developed by Joiris E et al. 1998. Pharm Res 15:1122-1130. Phase-pure crystals of LMH dihydrate, prism-shaped (S) an d plate-shaped (T), were prepared by adjusting the composition of the cryst allization solvent. At the same compaction pressure, T always gives stronge r tablets than S, (i.e.; the tabletability of T is greater). The porosity o f tablets from T crystals is always greater than that of S crystals when co mpressed at the same pressure, (i.e.; the compressibility of T is lower). T he tensile strength of T tablets, at the same porosity, is greater than tha t of S tablets, (i.e.; the compactibility of T is greater). Therefore, the greater tabletability of T is a result of its better compactibility that ov ercomes the negative effects by its lower compressibility. The greater comp actibility of T is related to favorable orientation of the slip planes in t he tablet, corresponding to greater plasticity under load. The yield streng ths of T and S crystals are essentially the same (20 MPa). Therefore, the c rystal shape influences the tableting performance but does nob, in principl e, affect the yield strength of LMH dihydrate. (C) 2001 Wiley-Liss, Inc. an d the American Pharmaceutical,Association J Pharm Sci 90:569-579, 2001.