Thermal analysis techniques cover all methods in which a physical property is monitored as a function of temperature or time, whilst the sample is being heated or cooled under controlled conditions. Calorimetric methods measure the energy involved in every process. The quicker new developments attain the market, such as the progression of micro or nanotechnologies, combinations of different hyphenated techniques, as well as the development of high automated or high throughput systems, the faster new horizons will open in the industrial environment. In addition, the application of sophisticated kinetic software in DSC, calorimetry and reaction calorimetry gives better safety predictions.
The determination of accurate thermodynamic data for the interactions of biomolecules has been enhanced over the last decade by the use of isothermal titration calorimetric (ITC) instrumentation. These instruments are now standard kits in many biophysical/structural biochemistry laboratories of pharmaceutical companies. Despite this, there is little evidence for the input of thermodynamic data into the drug development process.
Drug development involves the identification and subsequent optimisation of low molecular weight compounds with a desired biological activity. Often, the initial binding affinity of those compounds towards their intended target needs to be improved by five or more orders of magnitude before they become viable drug candidates; a process that would be greatly facilitated if the different forces that contribute to binding were experimentally accessible. Isothermal titration calorimetry (ITC) provides such a tool.
In the previous article (European Pharmaceutical Review, Issue 2, 2007) an introduction to calorimetry was given and its application to polymorph characterisation, discussed. Another area of application of growing importance is quantification of (usually small) amorphous contents. A requirement to demonstrate the presence or absence of amorphous material is becoming more important in regulatory documentation and calorimetric techniques are emerging as major tools in this arena. This article focuses on the use of various calorimetric techniques for quantifying amorphous content.
Characterising the properties of a material, understanding how these properties change in relation to local environment and quantifying potential interactions with other species are facets central to any drug development programme. Not understanding and, more importantly, not controlling these factors can have serious consequences for a pharmaceutical, from irreproducible processing to poor bioavailability, product instability and, worse, patentability. Properties that may be characterised include solubility, dissolution rate, stability (in combination with other excipients and as a function of relative humidity and temperature) and per cent crystallinity (or amorphous content).
Thermal analysis methods and coupled techniques are well established procedures in material science. Due to the different information delivered, thermal analysis methods are concurrent or complementary to other analytical techniques such as spectroscopy, chromatography, melting point determination, loss on drying, assay, for identification, purity and quantitation. They are basic methods in the field of polymer analysis and in physical and chemical characterisation of pure substances as well as for mixtures. They find best application for pre-formulation, processing and control of the drug product.
The determination of the key physical and chemical properties of a new material is essential. The melting point, glass transition temperature, the number and identification of the different phases it may have, and the temperatures at which they are formed are all of great value, not only in assessing its practical pharmaceutical potential but also as they can form the basis of many routine QC procedures.
Thermal analysis equipment can be found in nearly all of the analytical, development, formulation and QA laboratories within the pharmaceutical industry. However, these work horse instruments are learning to run faster and to analyse an ever more varied field of samples.
