Stability assessment of pharmaceuticals and biopharmaceuticals by isothermal calorimetry

The assessment of stability (of actives, excipients and/or formulated products) is an important, and often time-consuming, part of pharmaceutical product development. Conventionally, HPLC is used to quantify the concentrations of a parent compound and any degradation products as a function of storage time. HPLC, however, is relatively insensitive to small changes in concentration and it is often the case that stability assays are conducted under stress conditions, in order to accelerate any degradation processes. The Arrhenius relationship is then employed to give an initial prediction of stability under storage conditions while long-term studies, under storage conditions, are conducted to confirm these predictions. The properties of isothermal calorimetry, such as its intrinsic sensitivity to small changes in heat and invariance to the physical form of a sample, make it ideally suited for stability assessment because it obviates the need for an Arrhenius analysis. In addition, the ability to conduct titration or gas perfusion experiments vastly increases its range of applications. Recent advances in instrumental design and data analysis have made it easier to analyse data quantitatively for complex systems. It is the purpose of this review to highlight some of these developments, discuss them in the context of pharmaceutical and biopharmaceutical examples and explore some of the future challenges and applications of the technique.