Use of isothermal microcalorimetry in pharmaceutical preformulation studies,Part I. Monitoring crystalline phase transitions

Solid-state transformation kinetics of two crystal forms of a synthetic tetrapeptide was monitored by isothermal microcalorimetry and complementary solid-state analytical techniques. Form B, the crystal form obtained from the synthetic process transformed to Form D upon exposure to higher relative humidity conditions (>60% RH). The transformation occurred rapidly at higher temperature, and relative humidities. An intermediate phase of very low crystallinity (amorphous-like phase) was observed when transformation was slow. Form D was observed to be physically stable at higher relative humidities and thus the preferred crystal form for development. Exposure of Form B to high relative humidity was the only process through which Form D was obtained. Optimal conditions for transformation of Form B to Form D were determined by microcalorimetric experiments and were used for larger scale processing of Form B to Form D.     

Use of isothermal microcalorimetry in pharmaceutical preformulation studies,Part II. Amorphous phase quantification in a predominantly crystalline phase

Low amounts of amorphous phase present in predominantly crystalline powders were quantified by using various analytical techniques with an emphasis on the use of Isothermal Perfusion Microcalorimetry. The amorphous phase was plasticized using ethanol vapor and enthalpy of re-crystallization of amorphous phase was used for generation of a calibration curve. Amorphous content as low as 5% was quantified using this technique. Although baseline noise was very low, additional processes occurring during re-crystallization confounded quantification of lower amorphous fractions. This revised version was published online in July 2006 with corrections to the Cover Date.