Thermal analysis of glassy pharmaceuticals

The relevance of the amorphous state to pharmaceutical dosage forms: glassy drugs and freeze dried systems

“…In particular, the authors have discussed the significance of the ratio between the glass transitional and melting parameters, as T g /T m tends to be :0.5 for symmetrical polymers and 0.7 for asymmetrical (Gujrati and Goldstein, 1980), this refers back to the concept of fragile and strong glasses outlined in Section 2.2, although here the ratio is inverted. Kerc' and Src' ic' (1995) report values between : 0.6 and 0.8 for low molecular weight pharmaceuticals, which are slightly higher than those found for polymeric systems. According to the 'rule of thumb' of T m /T g ratios outlined earlier, this indicates that low molecular weight pharmaceutical systems are more fragile glass-forming systems than polymers.…”

“…12 for water-ethanol and water systems. Interestingly, these authors also studied the relaxation behaviour of the glassy system on storage below T g , showing that while quench cooled indomethacin was stable over a 2 year period at room temperature, pulverised (T g ) and melting point (T m ) data for a range of pharmaceuticals [reproduced from Kerc' and Src' ic' (1995)] Amorphous drugs may be prepared in a number of ways such as rapidly cooling from the melt or precipitation from suitable solvent systems. Drying or grinding may deliberately or accidentally induce amorphous characteristics.…”

“…Kerc' and Src' ic' (1995) have prepared a highly useful compilation of T g and melting point (T m ) data for a number of drugs which is reproduced in Table 1. It should be born in mind that the conditions under which the various samples were prepared and measured are highly unlikely to be uniform, hence absolute comparisons between data points may not be applicable.…”

“…Similarly, the reviews by Hancock and Zografi (1997) and Kerc' and Src' ic' (1995) are also recommended, the former containing a detailed discussion of the nature of the glassy state of pharmaceuticals and the latter placing emphasis on published examples of amorphous drug systems, with particular consideration of thermal analysis. Given the breadth that the topic of amorphous pharmaceutical systems has now assumed, it is not possible to cover all aspects of the subject in a single review.…”

Thermal behaviour of zircon/zirconia-added chemically durable borosilicate porous glass

“…T f is denoted as the onset glass transformation temperature, T mid is the midpoint, and T m is the maximum of the endothermic inflection. Kerĉ and Sĉiĉ considered another point after T m which they denoted as the extrapolated end temperature (T e ) [16]. T f and T mid are generally accepted as the glass transition temperature (T g ) for most applications [17].…”