Abstract
Temperature‐induced phase transitions in carbamazepine (CBZ) and 10,11‐dihydrocarbamazepine (DHC) were studied by simultaneous differential scanning calorimetry–X‐ray diffraction in this work. The transitions generally involve a transitional melt phase which is quickly followed by recrystallisation. The expansions of the unit cell as a function of temperature could be quantified and allow us to determine a directional order of stability in relation to the lattice constants. Dihydrocarbamazepine form II undergoes a conversion to form I by a localised melt phase. Carbamazepine (CBZ) form IV converts to form I at 182 °C, again by a localised intermediate melt phase. CBZ form II converted to form I at 119 °C by a pathway that appears to have included some melting, and form III underwent a part melt‐recrystallisation and a part sublimation‐recrystallisation to form I.
Highlights
Pharmaceutical materials may exist in many different physical forms, each of which will have unique physicochemical properties such as solubility, dissolution rate, stability, hygroscopicity, mechanical strength, flowability and compressibility.[1]
It is essential that as much as possible is known about the physical form of an active ingredient and how it will behave under different conditions before it can be used in the clinic
Variable-temperature X-ray diffraction (XRD) approaches have led to useful insights into physical form transitions in pharmaceutical materials, but standard lab instruments take a considerable time to record a diffraction pattern and so it is difficult to study transient or short-lived phases
Summary
Pharmaceutical materials may exist in many different physical forms, each of which will have unique physicochemical properties such as solubility, dissolution rate, stability, hygroscopicity, mechanical strength, flowability and compressibility.[1]. The most recently discovered form (V) is the only known polymorph of CBZ to pack catemerically, without forming dimers. In all cases form I was shown to melt at 192– 194 8C.[9] The discovery of CBZ V was achieved by templating crystal growth on the surface of a crystal of form II of 10,11-dihydrocarbamazepine (DHC) (Figure 1). The latter is a structural analogue of CBZ. For the first time, detailed studies into the polymorphism of DHC and CBZ, describing a number of new insights into the transformations between the various forms of each
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