Host-guest interactions between β-cyclodextrin and piroxicam

In order to obtain experimental evidence for the complexation between B-cyclodextrin and piroxicam (4-hydroxy2-methyl-N-2-pyridyl-2H- 1,2-benzothiazine-3-carboxamide-1,1-dioxide) and to investigate the thermodynamics of this interaction, a flow microcalorimetric study of this system has been undertaken. In fact, the mixing of beta-cyclodextrin and piroxicam in ratio 1:1 in given experimental conditions gives rise to a system showing better pharmacological properties than piroxicam alone. The results confirm the formation of a complex between beta-cyclodextrin and piroxicam and allow the evaluation of the equilibrium constant for the process, assuming the formation of a 1 : 1 complex. It results in log K' = 3.54, where K' is the apparent formation constant at pH 9.00, in good agreement with literature data for similar compounds. The values of Delta H and Delta S are also reported. (C) 1998 Elsevier Science B.V. All rights reserved.