Physicochemical Properties and Stability of Two Differently Prepared Amorphous Forms of Simvastatin

Abstract

The purpose of this work was to investigate possible differences in physicochemical properties and stability between amorphous forms of simvastatin prepared by (a) cryo-milling and (b) melting and quench-cooling. Both methods resulted in X-ray amorphous forms and HPLC analysis indicated a small percentage of chemical degradation during the preparation processes. Modulated differential scanning calorimetry (MTDSC) results showed significantly different onset temperatures of recrystallization and recrystallization enthalpies for both amorphous forms. Raman spectra of the amorphous forms showed differences in the intensities of the methylene bands for the cryo-milled and quench-cooled forms. Upon storage at 20 °C, the cryo-milled samples recrystallized within one day, whereas the quench-cooled samples showed no signs of recrystallization, even when stored at 40 °C for 3 days. Principal component analysis was carried out to further analyze any differences in the Raman spectra. The results indicate the existence of an amorphous form for the cryo-milled simvastatin that is spectrally distinguishable from the quench-cooled amorphous form. The thermodynamic parameters suggest that this form is less disordered compared to the quench-cooled form.