Piroxicam monohydrate

Grant and coworkers [8] studied the dehydration kinetics of piroxicam monohydrate using both model-free and model-fitting approaches in an effort to understand the effects of lattice energy and crystal structure. The dehydration kinetics was found to differ when determined under isothermal and nonisothermal conditions. Ultimately, the dehydration behavior of piroxicam monohydrate was determined by details of the crystal structure, which was characterized by an absence of channels and a complicated hydrogen-bonding network, and ab initio calculations proved useful in understanding the structural ramifications of the dehydration process. 

Many other examples could have been selected in the area of solvate investigation. Numerous reports of dehydration kinetic studies on drug hydrates are found in the pharmaceutical literature. An instructive recent case concerns piroxicam monohydrate (PM) [67]. Model-free kinetics showed that the dehydration kinetics of PM under isothermal and non-isothermal conditions were different. Complementary structural studies revealed a complex hydrogen-bonding pattern that was reconciled with the observed dehydration behaviour of PM. 

Piroxicam (Kozjek et al., 1985) is a particularly interesting example in which the transition temperature is 2SD. At physiologically relevant temperatures, the yellow monohydrate triclinic form is actually more soluble than the white monoclinic needle form. The anhydrous needles also... 

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