Pharmaceutical microcalorimetry: applications to long-term stability studies

Calorimetry has been a mainstay of stability analyses for some time in the form of differential scanning microcalorimetry (DSC). This technique exploits high (relatively) temperature studies of pure materials and of formulations to accelerate any degradation or interactions. The behaviour of the material at storage or ambient conditions is then estimated via extrapolation from the Arrhenius equation. Recent developments in isothermal microcalorimetry allow the direct determination of both kinetic and thermodynamic parameters for long, slow reactions from studies conducted at appropriate temperatures and under designated environmental control (pH, pO2, RH etc.). This review introduces the kinetic analysis of microcalorimetric data and, through selected examples, shows applications of the method.